Going down
Three layers, the seals between them, and when to try.
The underground is three layers, and they are sealed from each other. You do not drift from one into the next: there is a floor, it is called Stratum, and no tool in the game breaks it.
You will need
- Light, always — see The dark is not scenery
- Gear appropriate to the layer, which is what Fighting back and Gearing up are for
Steps
- Layer 1 runs from the stone line down about 2,100 cells. Copper, tin, coal, iron. The creatures here are the ones you meet first, and the layer's boss drops the Forge Core that becomes your Blast Furnace.
- Layer 2 runs from there to about 4,100 cells down. Hotter, and the creatures hit harder.
- Layer 3 is everything below that. All four of its creatures are heat tolerant well past the default, because the layer itself runs hot enough to kill something that is not.
Each layer's creatures are listed on the Creatures index, with a "Found" column that says which layers each one spawns in.
When it works
You arrive in a new layer with light, a way to fight, and something to carry ore home in — rather than arriving by falling and discovering all three are missing.
When it does not
You have hit a grey floor you cannot dig. That is Stratum, and it is supposed to stop you. It sits above every tool in the game by design — hardness 235, where the strongest thing you can swing reaches 210. The way down is not through it.
The heat is killing you. Layer 3 runs hot. Check what you are wearing: heat protection is a real stat on armour, and each item's page states its number in degrees.
Things hit much harder than they did one layer up. They do. Compare health and contact damage on the creature index, sorted by either column — the step between layers is visible as a number.
You fell a long way and died. Rope helps. So does not digging straight down, which is the thing everyone does once.
You cannot find the ore you came for. Ore is layer-dependent. Titanium and tungsten are deep, and they also need coke to smelt once you have them — check you can actually use a thing before you go a long way for it.
Next
Fighting back — because the deeper layers assume you can.