Fantasy Location: The Hidden Island
The Hidden Island is normally avoided by ships. It lays in the deep sea, surrounded by a pod of kraken. The island itself has two buildings on it. Both are submerged just a few feet under the water, so are a bit of a navigation hazard, especially during storms.
The two buildings are ancient temples. Each has a sundial inside centered inside. If someone moves one of the dials, they will hear a rumbling sound.
One dial actually raises the island out of the sea. Once it’s out of the water, it instantly starts growing plant life. Within six to eight hours the island is fully revegetated like it was never underwater. Once the island is out of the water, the second sun dial opens a previously hidden door. This dial does nothing if the island is still under water.
This opens into a Dwarven Village which has a secret passage down into the Underdark. The Dwarven city is unnamed and empty.
From the Dwarven City passages in the Underdark eventually lead to a drow city of 3000. It sits upon an huge underground sea. If someone manages to get to the middle of the sea, there is a huge whirlpool that goes upwards to the ocean. Entering the whirlpool takes someone to the ocean surface. During storms the whirlpool reverses and instead sucks objects from the sea above down in to the caverns.