In Trammel, the first level of Destard is a fairly large, cavernous area. It is occupied by mostly dragons, drakes and wyverns. There are also some water elementals to the east end, near a small body of water, as well as more to the north near another body of water.
Toward the west side of this level, are a number of giant serpents, and the entrance to Level 2 of the dungeon.
In Trammel, level two is occupied by much more dangerous monsters. Though you will still find wyverns, you'll also run into shadow wyrms (ouch), evil mage lords, daemons. All of the aforementioned monsters spawn in the South end of this level, save for wyverns, which spawn just about anywhere.
As you enter from the previous level, you will see the entrance to Level 3. So it is fairly easy to go between the three in an instant.
In Trammel, level three has more wyvern. But not just wyverns, as the Ancient Wyrm spawns to the East in a smaller chamber.