This mod focuses on adding caverns that randomly breach the depths of subway tunnels (if only sewers were an option, but they won't mesh up cleanly), expanding the underground with areas full of various flora, fauna, and strange encounters.

• Caverns of various sizes and randomized depths, with various debris, pillars, and other things to make the appearance more organic.
• Pools (including magma, of course), pockets of radiation, evidence of failed expeditions, buried ruins (mundane or otherwise), and stranger things can show up.
• Exotic underground "plants" that can be harvested at various periods of the year, with varied uses as well.
• A wide variety of cavern critters that can show up, at a fairly consistent spawn rate.
• Unique sprites for all terrain added (with a focus on still being visually distinct in the dark), and for almost all items added.

• Finales for caverns that reach maximum length.
• Changing surface caves to use a similar system.
• A scenario to allow diving into exploration.