diff --git a/src/layout.rs b/src/layout.rs
index df99884..ad3ee22 100644
--- a/src/layout.rs
+++ b/src/layout.rs
@@ -128,6 +128,30 @@ impl Default for DungeonLayout {
     }
 }
 
+impl DungeonLayout {
+    // Build an empty layout for the current packing mode.
+    pub(crate) fn empty(packed_rooms: bool) -> Self {
+        Self {
+            packed_rooms,
+            ..Self::default()
+        }
+    }
+
+    // Build a layout from generated rooms and corridors.
+    fn from_generated_parts(
+        rooms: Vec<Room>,
+        corridors: Vec<Corridor>,
+        packed_rooms: bool,
+    ) -> Self {
+        Self {
+            rooms,
+            corridors,
+            packed_rooms,
+            ..Self::default()
+        }
+    }
+}
+
 // Collect all room cells except those belonging to excluded room ids.
 pub fn blocked_room_cells(rooms: &[Room], excluded_room_ids: &[usize]) -> HashSet<(usize, usize)> {
     let excluded: HashSet<usize> = excluded_room_ids.iter().copied().collect();
@@ -184,19 +208,7 @@ pub fn generate_layout(
     let mut corridors = Vec::new();
 
     if cols < 2 || rows < 2 || target_room_count == 0 {
-        return DungeonLayout {
-            rooms,
-            corridors,
-            doors: Vec::new(),
-            windows: Vec::new(),
-            text_labels: Vec::new(),
-            start_markers: Vec::new(),
-            end_markers: Vec::new(),
-            trap_markers: Vec::new(),
-            monster_markers: Vec::new(),
-            packed_rooms: pack_rooms_without_corridors,
-            stairs: Vec::new(),
-        };
+        return DungeonLayout::empty(pack_rooms_without_corridors);
     }
 
     let mut min_size = min_room_size.max(2);
@@ -212,19 +224,7 @@ pub fn generate_layout(
     }
 
     if min_size == 0 || max_size < min_size {
-        return DungeonLayout {
-            rooms,
-            corridors,
-            doors: Vec::new(),
-            windows: Vec::new(),
-            text_labels: Vec::new(),
-            start_markers: Vec::new(),
-            end_markers: Vec::new(),
-            trap_markers: Vec::new(),
-            monster_markers: Vec::new(),
-            packed_rooms: pack_rooms_without_corridors,
-            stairs: Vec::new(),
-        };
+        return DungeonLayout::empty(pack_rooms_without_corridors);
     }
 
     let room_sizes = generate_room_sizes(
@@ -245,19 +245,7 @@ pub fn generate_layout(
 
     if pack_rooms_without_corridors {
         rooms = place_packed_rooms(&room_sizes, &room_edges, cols, rows, &mut room_rng);
-        let mut layout = DungeonLayout {
-            stairs: Vec::new(),
-            rooms,
-            corridors,
-            doors: Vec::new(),
-            windows: Vec::new(),
-            text_labels: Vec::new(),
-            start_markers: Vec::new(),
-            end_markers: Vec::new(),
-            trap_markers: Vec::new(),
-            monster_markers: Vec::new(),
-            packed_rooms: true,
-        };
+        let mut layout = DungeonLayout::from_generated_parts(rooms, corridors, true);
         apply_doors(&mut layout, seed, door_settings, cols, rows);
         apply_windows(&mut layout, seed, window_settings, cols, rows);
         return layout;
@@ -307,19 +295,7 @@ pub fn generate_layout(
     }
 
     if rooms.len() < 2 {
-        return DungeonLayout {
-            rooms,
-            corridors,
-            doors: Vec::new(),
-            windows: Vec::new(),
-            text_labels: Vec::new(),
-            start_markers: Vec::new(),
-            end_markers: Vec::new(),
-            trap_markers: Vec::new(),
-            monster_markers: Vec::new(),
-            packed_rooms: false,
-            stairs: Vec::new(),
-        };
+        return DungeonLayout::from_generated_parts(rooms, corridors, false);
     }
 
     let mut min_width = min_corridor_width.max(1);
@@ -366,19 +342,7 @@ pub fn generate_layout(
         }
     }
 
-    let mut layout = DungeonLayout {
-        stairs: Vec::new(),
-        rooms,
-        corridors,
-        doors: Vec::new(),
-        windows: Vec::new(),
-        text_labels: Vec::new(),
-        start_markers: Vec::new(),
-        end_markers: Vec::new(),
-        trap_markers: Vec::new(),
-        monster_markers: Vec::new(),
-        packed_rooms: false,
-    };
+    let mut layout = DungeonLayout::from_generated_parts(rooms, corridors, false);
     apply_doors(&mut layout, seed, door_settings, cols, rows);
     apply_windows(&mut layout, seed, window_settings, cols, rows);
     layout
diff --git a/src/main.rs b/src/main.rs
index d944f3a..a3919b9 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -72,11 +72,9 @@ impl Default for DungeonApp {
     // Build the app with persisted settings and a generated layout.
     fn default() -> Self {
         let settings = settings::load_settings().unwrap_or_default();
-        let layouts = generate_all_levels(&settings);
-        let results = populate_stairs(layouts, &settings);
         let mut app = Self {
             settings,
-            levels: results.iter().map(|(l, _)| l.clone()).collect(),
+            levels: Vec::new(),
             suppressed_auto_door_edges: HashSet::new(),
             undo_stack: Vec::new(),
             redo_stack: Vec::new(),
@@ -93,11 +91,8 @@ impl Default for DungeonApp {
             hover_level_idx: None,
             hover_stair_idx: None,
         };
-        for (i, (_, modified)) in results.into_iter().enumerate() {
-            if modified {
-                app.refresh_level(i);
-            }
-        }
+        app.levels = generate_all_levels(&app.settings);
+        app.refresh_stairs();
         app
     }
 }
@@ -170,33 +165,9 @@ impl eframe::App for DungeonApp {
             }
         } else if panel_result.new_level_clicked {
             self.push_undo_snapshot();
-            let level_index = self.levels.len();
-            let level_seed = seed::derive_seed(self.settings.seed, level_index as u64);
-            let layout = layout::generate_layout(
-                self.settings.cols,
-                self.settings.rows,
-                self.settings.room_count,
-                level_seed,
-                self.settings.min_room_size,
-                self.settings.max_room_size,
-                self.settings.square_rooms_only,
-                self.settings.min_corridor_width,
-                self.settings.max_corridor_width,
-                self.settings.corridor_randomness,
-                self.settings.dead_end_rooms_percent,
-                self.settings.pack_rooms_without_corridors,
-                door_settings_from_ui(&self.settings),
-                window_settings_from_ui(&self.settings),
-            );
-            let layout = populate_random_markers(layout, &self.settings);
-            self.levels.push(layout);
-            let results = populate_stairs(self.levels.clone(), &self.settings);
-            self.levels = results.iter().map(|(l, _)| l.clone()).collect();
-            for (i, (_, modified)) in results.into_iter().enumerate() {
-                if modified {
-                    self.refresh_level(i);
-                }
-            }
+            self.levels
+                .push(generate_level(&self.settings, self.levels.len()));
+            self.refresh_stairs();
             self.settings.active_level_index = self.levels.len() - 1;
         }
         if ctx.input(|i| i.key_pressed(egui::Key::Delete) || i.key_pressed(egui::Key::Backspace)) {
@@ -385,29 +356,34 @@ fn generate_all_levels(settings: &UiSettings) -> Vec<DungeonLayout> {
 
     let mut levels = Vec::with_capacity(level_count);
     for i in 0..level_count {
-        let level_seed = seed::derive_seed(settings.seed, i as u64);
-        let layout = layout::generate_layout(
-            settings.cols,
-            settings.rows,
-            settings.room_count,
-            level_seed,
-            settings.min_room_size,
-            settings.max_room_size,
-            settings.square_rooms_only,
-            settings.min_corridor_width,
-            settings.max_corridor_width,
-            settings.corridor_randomness,
-            settings.dead_end_rooms_percent,
-            settings.pack_rooms_without_corridors,
-            door_settings_from_ui(settings),
-            window_settings_from_ui(settings),
-        );
-        let layout = populate_random_markers(layout, settings);
-        levels.push(layout);
+        levels.push(generate_level(settings, i));
     }
     levels
 }
 
+// Generate one dungeon level from the current settings.
+fn generate_level(settings: &UiSettings, level_index: usize) -> DungeonLayout {
+    let level_seed = seed::derive_seed(settings.seed, level_index as u64);
+    let layout = layout::generate_layout(
+        settings.cols,
+        settings.rows,
+        settings.room_count,
+        level_seed,
+        settings.min_room_size,
+        settings.max_room_size,
+        settings.square_rooms_only,
+        settings.min_corridor_width,
+        settings.max_corridor_width,
+        settings.corridor_randomness,
+        settings.dead_end_rooms_percent,
+        settings.pack_rooms_without_corridors,
+        door_settings_from_ui(settings),
+        window_settings_from_ui(settings),
+    );
+
+    populate_random_markers(layout, settings)
+}
+
 fn clamp_dependent_settings(settings: &mut UiSettings) {
     if settings.min_room_size > settings.max_room_size {
         settings.max_room_size = settings.min_room_size;
@@ -514,10 +490,8 @@ impl DungeonApp {
         if self.settings.active_level_index >= self.levels.len() {
             return;
         }
-        self.levels[self.settings.active_level_index] = DungeonLayout {
-            packed_rooms: self.settings.pack_rooms_without_corridors,
-            ..DungeonLayout::default()
-        };
+        self.levels[self.settings.active_level_index] =
+            DungeonLayout::empty(self.settings.pack_rooms_without_corridors);
         self.suppressed_auto_door_edges.clear();
         self.reset_transient_state();
     }
@@ -526,14 +500,8 @@ impl DungeonApp {
     fn regenerate_layout(&mut self) {
         self.drag_state = None;
         self.suppressed_auto_door_edges.clear();
-        let layouts = generate_all_levels(&self.settings);
-        let results = populate_stairs(layouts, &self.settings);
-        self.levels = results.iter().map(|(l, _)| l.clone()).collect();
-        for (i, (_, modified)) in results.into_iter().enumerate() {
-            if modified {
-                self.refresh_level(i);
-            }
-        }
+        self.levels = generate_all_levels(&self.settings);
+        self.refresh_stairs();
         if self.settings.active_level_index >= self.levels.len() {
             self.settings.active_level_index = 0;
         }
@@ -882,6 +850,18 @@ impl DungeonApp {
         );
     }
 
+    // Sync stair placement across all generated levels.
+    fn refresh_stairs(&mut self) {
+        let results = populate_stairs(self.levels.clone(), &self.settings);
+        self.levels = results.iter().map(|(layout, _)| layout.clone()).collect();
+
+        for (level_idx, (_, modified)) in results.into_iter().enumerate() {
+            if modified {
+                self.refresh_level(level_idx);
+            }
+        }
+    }
+
     fn refresh_doors(&mut self) {
         if self.settings.active_level_index >= self.levels.len() {
             return;
diff --git a/src/startend.rs b/src/startend.rs
index 763bba6..ce76bb1 100644
--- a/src/startend.rs
+++ b/src/startend.rs
@@ -242,103 +242,126 @@ fn pick_room_index(available_rooms: &[usize], room_count: usize, seed_value: u64
 }
 
 pub fn populate_random_traps(mut layout: DungeonLayout, settings: &UiSettings) -> DungeonLayout {
-    if settings.trap_frequency_percent == 0 {
-        return layout;
-    }
-
-    let mut trap_markers = Vec::new();
-
-    // Rooms
-    for (idx, room) in layout.rooms.iter().enumerate() {
-        let seed = seed::derive_seed(settings.seed, TRAP_ROOM_STREAM_BASE + idx as u64);
-        if (seed % 100) < settings.trap_frequency_percent as u64 {
-            let count = random_range_inclusive(
-                settings.min_traps_per_area,
-                settings.max_traps_per_area,
-                seed.rotate_left(13),
-            );
-            for i in 0..count {
-                trap_markers.push(marker_in_room(
-                    room,
-                    1,
-                    1,
-                    seed.wrapping_add(i as u64).rotate_right(7),
-                ));
-            }
-        }
-    }
-
-    // Corridors
-    for (idx, corridor) in layout.corridors.iter().enumerate() {
-        let seed = seed::derive_seed(settings.seed, TRAP_CORRIDOR_STREAM_BASE + idx as u64);
-        if (seed % 100) < settings.trap_frequency_percent as u64 {
-            let count = random_range_inclusive(
-                settings.min_traps_per_area,
-                settings.max_traps_per_area,
-                seed.rotate_left(13),
-            );
-            for i in 0..count {
-                if let Some(cell) = pick_random_corridor_cell(corridor, seed.wrapping_add(i as u64))
-                {
-                    trap_markers.push(layout::AreaMarker { cell, size: 1 });
-                }
-            }
-        }
-    }
-
-    layout.trap_markers = trap_markers;
+    layout.trap_markers = populate_random_area_markers(
+        &layout,
+        settings.seed,
+        settings.trap_frequency_percent,
+        settings.min_traps_per_area,
+        settings.max_traps_per_area,
+        TRAP_ROOM_STREAM_BASE,
+        TRAP_CORRIDOR_STREAM_BASE,
+    );
     layout
 }
 
 pub fn populate_random_monsters(mut layout: DungeonLayout, settings: &UiSettings) -> DungeonLayout {
-    if settings.monster_frequency_percent == 0 {
-        return layout;
-    }
-
-    let mut monster_markers = Vec::new();
-
-    // Rooms
-    for (idx, room) in layout.rooms.iter().enumerate() {
-        let seed = seed::derive_seed(settings.seed, MONSTER_ROOM_STREAM_BASE + idx as u64);
-        if (seed % 100) < settings.monster_frequency_percent as u64 {
-            let count = random_range_inclusive(
-                settings.min_monsters_per_area,
-                settings.max_monsters_per_area,
-                seed.rotate_left(13),
-            );
-            for i in 0..count {
-                monster_markers.push(marker_in_room(
-                    room,
-                    1,
-                    1,
-                    seed.wrapping_add(i as u64).rotate_right(7),
-                ));
-            }
-        }
-    }
-
-    // Corridors
-    for (idx, corridor) in layout.corridors.iter().enumerate() {
-        let seed = seed::derive_seed(settings.seed, MONSTER_CORRIDOR_STREAM_BASE + idx as u64);
-        if (seed % 100) < settings.monster_frequency_percent as u64 {
-            let count = random_range_inclusive(
-                settings.min_monsters_per_area,
-                settings.max_monsters_per_area,
-                seed.rotate_left(13),
-            );
-            for i in 0..count {
-                if let Some(cell) = pick_random_corridor_cell(corridor, seed.wrapping_add(i as u64))
-                {
-                    monster_markers.push(layout::AreaMarker { cell, size: 1 });
-                }
-            }
-        }
-    }
-
-    layout.monster_markers = monster_markers;
+    layout.monster_markers = populate_random_area_markers(
+        &layout,
+        settings.seed,
+        settings.monster_frequency_percent,
+        settings.min_monsters_per_area,
+        settings.max_monsters_per_area,
+        MONSTER_ROOM_STREAM_BASE,
+        MONSTER_CORRIDOR_STREAM_BASE,
+    );
     layout
 }
 
+// Populate simple one-cell area markers in rooms and corridors.
+fn populate_random_area_markers(
+    layout: &DungeonLayout,
+    master_seed: u64,
+    frequency_percent: usize,
+    min_count: usize,
+    max_count: usize,
+    room_stream_base: u64,
+    corridor_stream_base: u64,
+) -> Vec<layout::AreaMarker> {
+    if frequency_percent == 0 {
+        return Vec::new();
+    }
+
+    let mut markers = Vec::new();
+
+    for (idx, room) in layout.rooms.iter().enumerate() {
+        let area_seed = seed::derive_seed(master_seed, room_stream_base + idx as u64);
+        append_room_markers(
+            &mut markers,
+            room,
+            area_seed,
+            frequency_percent,
+            min_count,
+            max_count,
+        );
+    }
+
+    for (idx, corridor) in layout.corridors.iter().enumerate() {
+        let area_seed = seed::derive_seed(master_seed, corridor_stream_base + idx as u64);
+        append_corridor_markers(
+            &mut markers,
+            corridor,
+            area_seed,
+            frequency_percent,
+            min_count,
+            max_count,
+        );
+    }
+
+    markers
+}
+
+// Add room markers when the room passes the frequency roll.
+fn append_room_markers(
+    markers: &mut Vec<layout::AreaMarker>,
+    room: &layout::Room,
+    area_seed: u64,
+    frequency_percent: usize,
+    min_count: usize,
+    max_count: usize,
+) {
+    if !passes_frequency_roll(area_seed, frequency_percent) {
+        return;
+    }
+
+    let count = random_range_inclusive(min_count, max_count, area_seed.rotate_left(13));
+    for offset in 0..count {
+        markers.push(marker_in_room(
+            room,
+            1,
+            1,
+            area_seed.wrapping_add(offset as u64).rotate_right(7),
+        ));
+    }
+}
+
+// Add corridor markers when the corridor passes the frequency roll.
+fn append_corridor_markers(
+    markers: &mut Vec<layout::AreaMarker>,
+    corridor: &layout::Corridor,
+    area_seed: u64,
+    frequency_percent: usize,
+    min_count: usize,
+    max_count: usize,
+) {
+    if !passes_frequency_roll(area_seed, frequency_percent) {
+        return;
+    }
+
+    let count = random_range_inclusive(min_count, max_count, area_seed.rotate_left(13));
+    for offset in 0..count {
+        if let Some(cell) =
+            pick_random_corridor_cell(corridor, area_seed.wrapping_add(offset as u64))
+        {
+            markers.push(layout::AreaMarker { cell, size: 1 });
+        }
+    }
+}
+
+// Check whether an area spawns markers.
+fn passes_frequency_roll(area_seed: u64, frequency_percent: usize) -> bool {
+    (area_seed % 100) < frequency_percent as u64
+}
+
 fn pick_random_corridor_cell(
     corridor: &layout::Corridor,
     seed_value: u64,