8.3 KiB
Underground System
Layer Stack
The map is a vertical stack of hex grids. Each layer shares the same coordinate system — hex (x,y) on the surface sits directly above hex (x,y) underground.
┌──────────────────────────┐
│ ETHER PLANE │ (future — magical dimension)
├──────────────────────────┤
│ SURFACE │ standard play layer
├──────────────────────────┤
│ UNDERGROUND L1 │ shallow caverns, mine networks
├──────────────────────────┤
│ UNDERGROUND L2 │ deep warrens, ancient ruins
├──────────────────────────┤
│ UNDERGROUND L3 │ abyss, primordial deep (late game)
└──────────────────────────┘
A Dwarf city's building tiers correspond directly to floors:
- Surface: Lv1 buildings (default)
- L1: second building slot (Excavation tech required)
- L2: third building slot (Deep Warrens tech required)
- L3: fourth building slot (Undercity tech required)
Underground Tile States
Underground space must be created before it can be used.
| State | Description | Building possible |
|---|---|---|
| Solid Rock | Default — no hollow space | No |
| Raw Cavern | Excavated or natural, rough | Yes (1 slot, reduced HP) |
| Finished Cavern | Shored with stone supports | Yes (full HP, stable) |
| Developed Chamber | Has buildings and workers | Yes (occupied) |
| Cracked | Structurally compromised | Existing buildings only |
| Rubble | Collapsed | No (must be cleared) |
| Void/Sinkhole | Full collapse, may breach surface | No (permanent) |
Excavation
Underground space is created through excavation. It is queued via the Mason Lodge and consumes production and stone materials.
| Action | Building req | Time | Cost | Requirements |
|---|---|---|---|---|
| Excavate L1 hex | Mason Lodge Lv1 | 4-6 turns | Prod + stone | Must own surface tile above |
| Shore L1 cavern | Engineer on tile | 2-3 turns | Materials | Raw Cavern must exist |
| Excavate L2 hex | Mason Lodge Lv3 | 8-10 turns | Prod++ + stone | L1 must already exist below that surface hex |
| Excavate L3 hex | Mason Lodge Lv4 | 12-15 turns | Prod+++ + stone | L2 must already exist |
Excavation can only happen below tiles you control on the surface. You cannot excavate under neutral or enemy land.
Natural Caverns
Natural caverns are pre-existing Raw Caverns discovered during exploration. They skip excavation cost entirely.
- Discovered by Scout, Explorer, or Cartographer moving through adjacent surface tiles
- Immediately buildable after claiming (no excavation required)
- Natural caverns frequently extend beyond surface borders into neutral or enemy territory
- Cavern territory that extends past your surface borders is unclaimed — another player's Scout could find the same network from another entrance
Underground border disputes are resolved the same way as surface borders: culture expansion, Pioneer preparation, or tile purchase. The underground is not automatically yours because the surface above it is yours.
Connection Points
Units move between layers through connection points.
| Type | Who can use | Notes |
|---|---|---|
| Mine shaft | Any unit (with underground movement tech) | Built by Engineer on owned tile |
| Natural cavern entrance | Any unit | Discovered by Scout/Explorer |
| Tunnel Sapper dig | Tunnel Sapper only | Creates new connection, takes turns |
| Siege Drill breach | Heavy units | Violent entry — connection collapses after use |
| City internal descent | Any friendly unit inside the city | Dwarf cities have internal access to all their floors |
Underground Terrain Types
| Terrain | Movement | Yield | Combat modifier |
|---|---|---|---|
| Cavern | Normal | Production | Standard |
| Lava Tube | Fast | — | Extreme heat (damage per turn without heat protection) |
| Underground River | Blocked without bridge | Food | — |
| Deep Ore Vein | Normal | Production++ | — |
| Ancient Ruins | Normal | Gold | Discoverable loot |
| Mushroom Forest | Slow | Food | +cover |
| Collapsed Tunnel | Impassable | — | Must be cleared by Engineer |
Structural Integrity
Underground tiles have HP that can be degraded from above (surface siege) or below (cave-in events).
Collapse Chance per Hit (Surface Siege → Underground)
| Surface terrain | Collapse chance per siege hit |
|---|---|
| Plains | 40% |
| Hills | 25% |
| Mountain | 10% |
More hollow space below = higher collapse chance modifier. A tile with L1 + L2 + L3 all excavated is significantly more vulnerable than a tile with only L1.
Accumulation
Collapse does not happen instantly. Damage accumulates:
| Hit count | Result |
|---|---|
| 1st hit | Crack — structural damage, buildings take -20% HP, units take light damage |
| 2nd hit | Partial Collapse — one underground floor destroyed, units on it killed, buildings rubbled |
| 3rd hit | Full Collapse — all underground floors crushed, surface tile begins sinking |
| Critical (massive siege) | Instant Collapse possible at high enough tier siege |
Cascade
When a tile fully collapses, structurally connected adjacent tiles may follow:
- Each adjacent hollow tile rolls for cascade collapse (25% base chance)
- Reinforcement tech (Pillar Engineering) prevents cascade — each tile fails independently
- A key load-bearing hex collapsing can trigger a chain that swallows an entire city quarter
The Breach
When a surface tile sinks and L1 collapses beneath it, the underground becomes visible and accessible from the surface. The ravine punches through both layers.
- Units can descend into what was the underground city without a mine shaft
- The breach is visible to all players — no fog of war on an open hole
- Defenders must now protect the breach as a new entry vector
- The breach can be partially blocked by filling rubble (costly Engineer work)
- A full Sinkhole permanently exposes the underground to the sky
Collapse as a Weapon
Offensive: Bombard adjacent cavern tiles rather than the fortified surface. Cascade collapse destroys the city's economic foundation while the surface garrison is still standing.
Defensive: When enemy Tunnel Sappers advance underground, collapse the tunnel ahead of them. Cost: your tunnel and any ore veins on that path. Benefit: advance permanently stopped.
Trap: Deliberately leave underground hollow near your border. When enemy units advance through it, collapse the ceiling. Units inside are buried.
Attack Vectors into an Underground City
| Method | How | Counter |
|---|---|---|
| Surface assault | Standard attack on surface tile | Wall + garrison |
| Tunnel infiltration | Find natural cavern entrance, send units with underground movement | Underground patrol, collapse tunnel |
| Sapper breach | Tunnel Sapper digs new tunnel over several turns | Counter-mining (Demolitions Expert), underground patrols |
| Siege Drill breach | Siege unit drills from adjacent tile, single-use | Detect and attack the drill before breakthrough |
| Mine shaft seizure | Capture the surface mine entrance tile | Defend the shaft OR collapse it (destroys your own mine) |
Reinforcement Tech Tree
| Tech | Effect |
|---|---|
| Stone Shoring (early) | +20% structural integrity on all underground tiles in owned territory |
| Pillar Engineering (mid) | Prevents cascade collapse — tiles fail independently |
| Blast Dampening (mid) | -30% collapse chance from surface bombardment |
| Deep Foundation (late) | Developed underground tiles treated as Mountain terrain for collapse purposes |
| Sealed Warrens (late) | Can manually seal underground hexes — converts to Solid Rock permanently (pre-emptive) |
Without Pillar Engineering, one well-placed siege barrage that collapses a load-bearing tunnel can take down an entire city block. It is a high-priority defensive investment.