Vanaheim is a Wrath of Stormheart expansion-only location.
It's the sacred place where old dragons come to spend their last days, and dragon bones are found in mounds on the island. It's built around an ancient skeleton of a Bewilderbeast.
It is guarded by the Sentinel dragons, that make sure no stranger come to the island and break the solemn peace of the place. One of those enemies are the Grim Gnasher, that come to prey on the weak dragons.