If my research is correct, the island in the map below is called “Treasure Island.”
Treasure Island is an island in Mindemoya Lake. Mindemoya Lake lies on Manitoulin Island. Manitoulin Island is in Lake Huron (one of the Great Lakes). Therefore, Treasure Island is an island in a lake on an island in a lake. It’s not the only one, but it’s one of the largest.
To take things a step further, Vulcan Point is a small island in Crater Lake, which lies on Volcano Island, which is in Lake Taal, which is on the island of Luzon in the Philippines. Therefore, Vulcan Point is an island in a lake on an island in a lake on an island.
I don’t know why I find this stuff so interesting…