The helpfile says:
"Thieves and assassins with this edge may conceal themselves effectively within
the subterranean realm they call home.

Only races born to the sunless world may choose this edge."

I took this edge, but noticed that it didn't let me sneak while hidden. E.g., moving from room to room while hidden.

Is this by design? If so, why?

Thanks

Yes. You can hide there, but it works like wilderness hide for assassins does... since it's wildernessy.

Under the explanation that it's their actual "hometerrain"?

It can be changed, I just don't think it should be.

That would be a pretty sickening boost to any roguish chars in the underdark. What I wouldn't mind seeing, though, if it's feasable, and you really wanted to do it, would be a 2nd edge on top of that, which if you *REALLY* felt the underdark was your hometerrain, switches where you can sneak through. You can sneak through the underdark, but if you spend *SO* much hometime down there, you can't sneak through the surface world anymore.

I'd probably RP a lot more lol