Ustengrav is a Nordic ruin located north-east of Morthal. The approach is guarded by bandits and mages.
Inside are more bandits, mages and draugr as well as a copy of the spell tome for Conjure Flame Atronach.
The Depths are where the Dragonborn expects to find the Horn of Jurgen Windcaller but instead finds only a note. This is a surprisingly vast underground forested area and also the location of a word wall containing one of the words of power for the shout "Become Ethereal". Next to the word wall is a small pool with a waterfall. Behind that waterfall is a small treasure room guarded by a draugr.