Going down
Prepare for the layers below the surface.
The underground has three layers, separated by Stratum. You cannot dig through Stratum: its hardness is 235, and the strongest tool reaches 210. Look for another way down when you hit it.
Before you descend
Bring light. If you need a setup, see Lighting dark areas. Bring a weapon and armour suited to the creatures in the layer. Fighting back and Gearing up cover both.
Use rope for long drops, and avoid digging straight down. It is easy to fall farther than you meant to.
The layers
- Layer 1 starts at the stone line and runs about 2,100 cells down. You can find copper, tin, coal, and iron here. Its boss drops the Forge Core used to make a Blast Furnace.
- Layer 2 runs from there to about 4,100 cells down. It is hotter, and its creatures hit harder.
- Layer 3 lies below Layer 2. It is hot enough to kill an unprotected player. All four of its creatures tolerate much more heat than the default.
The Creatures index shows where each creature spawns. You can also sort it by health or contact damage before you enter a new layer.
Ore depends on the layer. Titanium and tungsten are deep underground. Titanium smelts in a fuel fire, but tungsten needs coke. Check what you need to process the ore before making a long trip for it.
If the heat hurts you in Layer 3, check the heat protection on your armour. Each item's page gives the protection in degrees.