Skull Cavern

The door

The Skull Cavern is in the northwest of the desert. The door stays locked until you have the Skull Key from floor 120 of the Mines.

There is no practical floor limit, and there is no elevator. Every visit starts on floor 1. Each floor has a ladder at the spot where you arrived, and that ladder leaves the cavern. The floor layouts are the same set the Mines use.

High luck makes ladders and shafts show up more often. Going down to floors where iridium nodes are more common is the efficient way to get ore. A stack of staircases fits 999 in one slot. Placing them still spends time, so a deep staircase drop leaves less of the day for mining.

• StrategyFood, shafts, and staircases
• A cavern dayWhat to bring before you go in
• The MinesWhere the Skull Key is

Iridium and quests

The chance of iridium ore rises slowly as you descend, and it rises quickly from floor 10 to floor 100. Monsters here can also drop iridium ore, iridium bars, and the same special items the Mines use.

The day after you first enter, Mr. Qi's letter starts Qi's Challenge. Reach floor 25. The reward is 10,000g by mail the next day. If you hit floor 25 on the first visit, the quest completes the next day anyway.

Qi's Hungry Challenge, from the Walnut Room on Ginger Island, asks for floor 100. Food and drink cannot be used inside the cavern while it is active. Buffs you ate before entering stay. Big slimes can carry hearts that heal 10 health. Staircases are allowed. The reward is 25 Qi gems.

Skull Cavern Invasion is another Walnut Room order for floor 100. Monsters are the stronger set, and radioactive nodes can spawn. Staircases are allowed. The reward is 40 Qi gems. After the first clear, the statue by the entrance toggles hard mode. The statue cannot be toggled while the quest is active, so set it before you accept the order. Difficulty is 0 with neither effect, 1 with the statue or the quest, and 2 with both. Each level adds 0.1% to the radioactive ore chance and 2% to the chance a monster spawns. At difficulty 2, most monsters have three times their base resilience. Health and damage rise as well.

Time and passing out

An in-game hour lasts 54 seconds in the Skull Cavern and 43 seconds outside it. Multiplayer, and prehistoric floors, keep the 43-second hour. You get more real time before 2:00 am. Food buffs are counted in game time, and that countdown is shorter in the cavern. Machines at home keep their normal clocks. Honey set in a keg at noon is still mead at 10:00 pm.

Empty health wakes you later the same day in Harvey's Clinic, charges 1,000g for the surgery, and can take several items. Passing out at 2:00 am costs 1,000g or 10% of your money, whichever is less.

Monsters

Dangerous caverns replace several of these with tougher versions, including the royal serpent. That form is only present while the cavern is dangerous.

Prehistoric floors and treasure rooms

A prehistoric floor is an infested floor, so every enemy has to die before a ladder appears. Pepper rex are the main threat. Mutant flies and iridium bats can spawn too. Dinosaur eggs and fiddlehead ferns can be foraged. Cutting the foliage can yield an ancient seed. From floor 7 downward, the chance to enter a prehistoric floor is about 2.2%. Time on these floors uses the normal 43-second hour.

Treasure rooms can appear from floor 10 down. The chance when you enter a floor is 0.01 plus daily luck divided by 10 plus luck buffs divided by 100. That is a 1% base. Daily luck moves it by up to 1% either way. The Special Charm adds 0.25%. Each point of food luck adds 1%. In multiplayer the luck is the average of the players in the cavern. Floor 100 always has a treasure chest, except on the run where you finish the cavern's secret. Floor 200 always has two chests. Floor 300 always has three.

Iridium nodes have a 3.5% chance to drop one Prismatic Shard. Mystic stones, from floor 100 down, drop 1–3 iridium ore, 1–4 gold ore, and a 25% chance of one Prismatic Shard.

• Shafts, food, and staircases
• Nodes, including mystic stones