Idle Deepcore Dig forever, profit while away

It starts with a pickaxe and a few hundred clicks, until you can afford a jackhammer that never gets tired. From there the machines take over: steam drills, seismic hammers, excavators, mechanical worms, each hitting harder and wider than the last. You can run a whole row of them at once, and the rock gets harder the deeper you go, so they had better. Once the drills are in place, the manual digging fades away and the job becomes watching your machines tear through the ground at speed. The drilling sounds are a quiet pleasure in themselves, and there is real satisfaction in a column of rock vanishing block by block.

Raw ore is not worth much, so you build furnaces: a stone kiln first, later a fission furnace. Copper and tin become bronze, iron becomes steel, crystals become lenses, uranium becomes fuel rods. Then you decide what each ingot is for. Sell them for cash, or feed them back into bigger machines and deeper mines. It is a light but real layer of planning, deciding whether this batch goes into your wallet or into the next upgrade. Furnaces are expensive, so early on you will sometimes dig faster than you can smelt, and the pile of ore waiting for the kiln becomes its own kind of progress bar.