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