Skull Cavern
Skull Cavern is located in the northwest area of the Desert. It is initially locked and requires the Skull Key to gain access. After entering the Cavern for the first time, a letter is received on the following day, from Mr. Qi. The letter begins the quest Qi's Challenge, which is completed by reaching floor 25 in the Skull Cavern. Completing the quest awards 
10,000g (Delivered by mail the following day).
There is no limit to the number of floors, or levels, in the Skull Cavern (at least until the integer limit of 2147483647 is reached). Similar to the Mines, the player advances through floors in the Skull Cavern by finding a ladder on each floor, either by mining rocks or defeating enemies. The player can sometimes find a shaft, or hole, which makes it possible to skip 3-15 floors. Jumping down the shaft causes health damage equal to 3x the number of levels skipped (although jumping down a shaft will never reduce health to less than 1). Unlike the Mines, there is no elevator to save progress, but on every floor there is a ladder at the starting point where you can leave the Skull Cavern. Each visit must start again from the first floor. If the player runs out of health or blacks out while exploring Skull Cavern, they will wake up sometime later on the same day, in Harvey's Clinic. A fee of 1,000g will be deducted for emergency surgery. Some items may also be lost.
Every ten floors the chance to find Iridium Ore increases significantly. The monsters in the Cavern also have a chance to drop ore and Iridium Bars. It can be a good idea to bring the Lava Katana or Galaxy Sword, as enemies are particularly strong. As with many other things, high Luck increases the frequency of ore veins, item drops, and the appearance of ladders/holes. Exploring the Cavern on a lucky day will increase the odds of finding loot and ladders. Since the frequency of Iridium Ore increases for every 10 floors descended into the Cavern, rapid descent is often more efficient for acquiring ore than thorough exploration. With a full bag of stone, it's possible to descend to floor 300+.
The plaques that can be occasionally found on the walls contain enciphered messages.
Preparation
Food
Useful food for exploring the Skull Cavern:
Explosives
Bombs make quick work of densely-clustered stones and ore veins. They're also necessary for permanently defeating Mummies.
- Buy Cherry Bombs from the Dwarf for 300g or craft them with 4 Copper Ore and 1 Coal.
- Buy Bombs from the Dwarf for 600g or craft them with 4 Iron Ore and 1 Coal.
- Buy Mega Bombs from the Dwarf for 1,000g or craft them with 4 Gold Ore, 1 Solar Essence, and 1 Void Essence.
The Slingshot's Explosive Ammo is also effective in dealing with small groups of stones, Iridium Ore deposits, and incapacitated Mummies. Loading the Slingshot with Gold Ore deals substantial damage, making it potentially useful for dispatching tough targets. Explosive ammo can be crafted or bought at the Adventurer's Guild for 100g.
Staircase
- Staircases can be used for rapid descent or skipping troublesome floors. Since staircases do not stack, it can be more space-efficient to bring plenty of Stone and craft the staircases as needed.
Rings
Warp Totems
- A Warp Totem can be used to make a quick exit if supplies are running low or the day is almost over.
Monsters
| Image | Monster | HP | Damage | Notes |
|---|---|---|---|---|
 |
Armored Bug | 8 | Cannot be killed. | |
 |
Big Slime | 60 | 5 | Splits into smaller Slimes when killed. Big Slimes are always purple in the Skull Cavern. |
 |
Purple Slime | 410 | 28 | Can drop Iridium Ore, Iridium Bar |
 |
Lava Bat | 80 | 15 | Appears rarely; flies. |
 |
Mummy | 260 | 30 | Needs to be finished with a bomb of any type after being knocked out with other weapons. If a bomb does enough damage to knock the Mummy out, it will also destroy it. |
 |
Serpent | 150 | 23 | Moves quickly; default flying enemy. |
 |
Iridium Bat | 300 | 30 | Appears at level 50+. Very high HP and Damage. |
 |
Iridium Crab | 240 | 15 | Appears at level 26+. |
 |
Carbon Ghost | 190 | 25 | May appear on Mummy levels. |
Treasure Rooms
Small rooms containing treasure chests, similar to those in The Mines, can randomly appear at level 10+. Daily luck and Luck Buffs affect the chance to find Treasure Rooms. Obtaining the Special Charm also increases the chance to find Treasure Rooms.
Below is a collapsable table of all possible treasures that can be randomly found inside Treasure Chests in the Skull Cavern.
Secret
After reading Secret Note #10, the player will find Mr. Qi at level 100 of the Skull Cavern. A cutscene ensues in which:
| Details |
|---|
| Mr. Qi will either congratulate the player for reaching level 100 while using 10 or less Staircases or say the player is "clever" but not "honorable" for using more than 10. In either case, he will award the player with Iridium Snake Milk, which permanently increases the player's Health by 25 points. |
History
- 1.3: Added Carbon Ghost, Iridium Bat, Iridium Crab, treasure rooms, and encounter with Mr. Qi. Removed exploit that allowed the player to avoid bomb damage by consuming food after placing a bomb.
| Locations | |
|---|---|
| Locations | Backwoods • Beach • Bus Stop • Calico Desert • Cindersap Forest • Farm • Farm Cave • Farm Pond • Graveyard • Ginger Island • Mastery Cave • Minecart • Mines • Mountain • Mutant Bug Lair • Pelican Town • Quarry • Quarry Mine • Railroad • Secret Woods • Sewers • Skull Cavern • Summit • Tunnel • Volcano Dungeon • Witch's Swamp |