Haetar's Cave is a location added by Wyrmstooth.
Haetar's Cave is a small ice cave and Nordic ruin within the glaciers south-east of Wyrmstooth Barrow. The remains of a group of Thalmor spies can be found here, having been slaughtered by Alberthor's controlled draugr.
The legs of Vulom and a word of the Phantom Form shout can be found here. If doing the quest "Unwanted Guests" for Alberthor, the Dragonborn will encounter additional Thalmor who have been sent to investigate the remains of the initial group.
Approaching the word wall will trigger a draugr overlord.