I like the idea a lot. I'd maybe tie it to ideas of corruption. Older fantasy is full of races who turned from morality/god/the gods/the light/righteousness/etc. and became twisted, ugly and evil. Dungeons might be something similar, but for places. Wherever evil happens, nature becomes more dangerous. Darker, at first, with bad weather, dangerous or rotting vegetation and hostile animals, then eventually, the landscape twists and dungeons begin to form.