Serathis: The Storm of Memory
Stonepile Lake is in the center of Serathis, and has an island devoid of all life in the center. Many rumors surround this island, and the stone ruins on it; it is said that those who foolishly explore it never return. The island itself seems to be safe enough; young men sometimes row out to it in a foolish attempt to show bravery, and merchants and fisherman even use it as a place to weigh anchor for lunch or to make repairs. However, under the ruins there is an opening, and any living thing that enters disappears with a green flash.
When the party visited the island they found that their magic was greatly amplified and perverted. For instance a constitution boosting spell caused Udyr to grow dangerously large and to grotesque proportions.