This article is a
The Korlasz Family Tomb is the initial dungeon in Siege of Dragonspear.
The crypt has two levels, upper and lower, you may not return to either of them once you choose to return to surface with Imoen.
Ammon is located in the first room and selecting friendly/neutral dialog choices will result in the Tome of Great Value quest. The cobalt moss is in a room on the same level but you may need to complete the second level first and climb the rope to access it. See the article on Ammon for more details.