From the nighttime views of the island under attack in Shell Shocked, Part 1, Berserker Island appears to be a very rocky, bare island. It is very 'vertical', having a tall central mountain with very little spread of hills of fields around it.
More detail is revealed in "Something Rotten on Berserker Island". The rocky central island is surrounded by significant sea stacks. The island has trees and grass, and a large amount of white-flowering bushes closer to the village proper. The interior of the island has a "maze of caves", in which ice structures can be found, extremely similar in appearance to Bewilderbeast ice.
All Dragons on the island are seen to act strangely - getting disoriented and not listening to their riders - when getting close to Berserker village, but not above a certain altitude. Given the strange ice-like formations in the underground caves of the island, it is entirely possible that a Bewilderbeast is present on the island. This also may help to explain Heather's Dragon Eye Lens and its relation to the Kking of Dragons' mentioned by Johann in "Sins of the Past".
Though it doesn't appear in game, Dagur mentions Berserker Island during a quest in the expansion Rise of Stormheart.