Apologies for the late reply, seems this one went unnoticed?
Yes movement to/from a Dungeon is Under-deeps movement. So indeed, descending is easy (= no roll), moving up is difficult.
Hmm, I searched for any specific info on The Under-galleries to see if that came up anywhere. It hasn't. It's not on the Under-galleries site card eithers. So apparently it's assumed clear (or obvious?) that MPs received from a site in your MP pile are Miscellaneous. I agree it's not stated explicitly anywhere, but what other type could they be?
Stone-age did not end because man ran out of rocks.