Lycanwing Island is, like most islands, a rocky place with tall cliffs. For the most part, only a large cavern is shown in the show. We do see, however, that there is at least some vegetation — evergreen trees.
Tuffnut is bitten by a mysterious beast in "Bad Moon Rising", which Gobber theorizes that the culprit is the fabled dragon species known as the Lycanwing. When Hiccup and Fishlegs find information about the Lycanwing on a Dragon Eye lens, they go to Lycanwing Island to investigate.
Hiccup and Fishlegs discover that the Lycanwing is just a myth to keep people away from two additional hidden Dragon Eye lens. They return promptly to Dragon's Edge before Tuffnut can cause any damage to himself from believing the Lycanwing myth.