Deep Drill
Deep Drill is built around an automatic drilling loop in which your goal is to turn dug metres into ore, then ore into progress. First, you distribute your earnings across twelve upgrade paths for the facility, increasing drill-bit speed, handling rock hardness more effectively, collecting more valuable resources, or preparing better income after a long absence. Then you let the shaft advance and assess the value of each investment. Since rewards depend on the distance covered rather than the time elapsed, a difficult layer also becomes less profitable. All eight successive strata are harder and less rewarding than the ones above them.
Otherwise, when progress slows to the point where further spending is no longer worthwhile, you seal the shaft to begin a new attempt. You then start again from zero in terms of depth, ore, and facility levels, but receive hearts based on your depth record. These hearts are spent on twelve permanent nodes that remain after a reset. Among other things, you can choose speed bonuses, protection against hardness, a shortcut through old workings, and a manager who can purchase levels while you are away. Heart gains strongly encourage a deep expedition, so you must decide whether to secure your progress or keep drilling until you reach its true limit. Have fun!