Does this feat work in the underdark? If so what would be considered the "wilderness"?

Thanks.

Unfortunately, as best as we can tell (and, again, I only tested briefly, so feel free to test more in depth) the druid/ranger wilderness feats are hardcoded to be determined by tileset, not the artificial/natural setting. So, unfortunately, these feats aren't much good in EfU.

However -

(1) Druids/rangers get access to special shops and equipment (2) We may look into scripting a way around this at some point. (3) Most areas already have modifiers to stealth, making it so you can actually effectively hide in a dark cave much better already (although this is universally applied).

Did some digging online but I couldn't find anything else other than what you mentioned (wilderness area is tied to tileset) Thanks for the info though.