Lake Voulismeni in the centre of town is the most famous landmark of Agios Nikolaos for visitors and locals alike.
Voulismeni has distinctive vertical walls reminiscent of a volcanic crater, which is why some people believe that it was created by a sunken volcano.
Today, the circular lake of Agios Nikolaos, 137 m in diameter and 64 m depth, has many cafés and restaurants set out around it.
The Voulismeni Lake connects to the harbour of the town by a channel dug since 1870.
According to legend, the goddess Athena 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.