Dig to the Weirdest World

A drilling game that keeps going down. You steer a rig through earth, collect what is in it and sell the cargo to buy power, energy and storage, which is what lets you reach the next layer before the energy runs out. Twenty-nine underground worlds get progressively less geological — crystal caves, giant mushrooms, lava, and places that are frankly not explicable — and eight rigs with shockwave, turbo and scanner abilities open as you go. Twenty-five quests give the descent a shape.