The Undercity: Tunnels, Bad Air, Bosses and the House Reserve

Under the whole map lies the Undercity: a tunnel network where fifteen thousand people once lived. It's split into three depths, Upper, Mid and Deep, and the deeper you go, the harder the dead and the better the loot. You need to be level 5 or higher.

Finding a way in

• Landmarks: the easiest entrances are marked by a giant rock hand or a huge stone skull that you can see from across a valley. There are about 20 on the map.
• Holes in the ground: there are many smaller entrances too. Some are gentle slopes; some are straight drops, so look before you jump.
• Your map marker: when you reach level 5, the House whispers to you and marks the nearest entrance on your map.

Bad air: the real danger

The deeper you go and the longer you stay, the worse the air gets:

Climbing is the only cure. As soon as you start shedding exposure, the damage stops.

Charcoal Filters give you about 10 minutes of clean air. The bad air still builds while it's on, so be climbing before it runs out. Craft them from 2 cloth and 4 coal (it makes two). The big dead grey trees in the burnt forest are full of coal, and the tunnel walls have charcoal in them too.

The Pit Boss miner's set

For real deep runs, craft the Pit Boss set at a workbench. Each piece costs 75 white chips, 10 red chips, 50 forged iron and 5 leather, paid with the real chips in your backpack, not your bank. Quality goes up with your heavy-armour crafting skill.

What's down there

• Caches: an Undercity Cache in the upper tunnels, a Strongbox in the middle depths and a Vault Cache in the deep. The better the cache, the more likely something is guarding it, and the dead often come for you as you walk up to one.
• Ambushes and patrols: packs of zombies wander the tunnels, and some lie in wait.
• Traps: spike pits, covered pits and drop shafts. Walk, don't sprint.
• Underground towns: a handful of settlements carved into the rock, each with its own cavern.
• The deep trader: somewhere in the deep there's a trader in a huge cavern. Nothing tells you where it is; you have to find it.
• The House Reserve: a sealed steel vault in the deep workings. Cut, blast or dig your way in. It reseals and restocks about every two weeks, so it's a race: whoever gets in first takes the best of it.
• The Ventilation Plant: one per map, deep down. Throw the breaker in its control room and the plant comes online for the whole server, permanently. After that, bad air builds only half as fast within 300 metres of it, which makes it the base camp for deep runs. Waking it also wakes the dead who stayed to run it.

The bosses

Six district bosses, each with its own kind of minion:

Kill the minions first, then turn on the boss.

The One Below waits in the deep chamber. It's the hardest thing underground: go with a group, and expect to be pulled toward it. It's the only source of The Mark From Below.

The story: The House Below

The quest line starts on its own when you finish First Light, and the first quest marks your nearest way down.

Chapter I: What They Left

1. Cold Storage: bring back a city record from a cache in the upper tunnels.
2. Down the Ledger: find a camp in the middle depths and bring back its log.
3. Below the Ledgers: recover the last page anyone wrote.
4. The Ones Who Went Deepest: kill one of the six district bosses.
5. Standing Below: come up and report.

Chapter II: What Is Still Down There

1. The Fans Stopped: find the Ventilation Plant and bring back its log.
2. The House Reserve: break into the sealed vault and bring something out.
3. The One Below: kill the thing in the deep chamber.

Tips

• Know your way out. Remember how you came in before you go deeper.
• Carry a spare filter even when you have one running.
• Bring a group for the deep. Vault Caches and bosses are built for more than one player.
• Bank your chips first. Anything you carry down can be lost.