Lake Voulismeni is a former sweetwater lake, later connected to the sea, located at the centre of the town of Agios Nikolaos. It has a circular shape of a diameter of 137 m and depth 64 m. The locals refer to it as just “the lake”. The lake connects to the harbour of the town by a channel dug in 1870. A panoramic view of the lake can be seen from a small park situated above it.
According to legend, the goddess Athena and Artemis bathed in it. Every year at midnight turning to Orthodox Christian Easter day, the majority of the population of the town gathers around the lake to celebrate with fireworks, and firecrackers thrown by the people attending that highlight event.
It was reported that the German army during their withdrawal from the area at WW2, disposed parts of their weaponry and/or vehicles into the deep lake.
A local urban legend has it that the lake is bottomless. Based primarily on locals noticing disturbances at the surface of the water during the Santorini earthquake of 1956, many assume a possible geological relation of the two locations.