If swimming pools and ponds have become too mainstream for a quick swim, perhaps it’s time to take a dip in the crater of an ancient submerged volcano, such as this natural lagoon on the Islet of Vila Franca do Campo in Portugal.

This tiny island is a rocky crater formation off the coast of Sao Miguel. Its main attraction is the circular lagoon on the islet, which is broken up by a tiny channel that connects it with the ocean. The result is a clear and calm pool that is perfect for swimming and diving. 

The islet and this natural pool are accessible only during the summer and their stunning geography has made them a popular destination. Erosion through continuous exposure to wind and water have created different rock formations around the islet, including a fascinating column-like structure.

Over the years, the islet has helped whalers spot their targets and has also served as a military fort. In 1983, the unique location was declared a nature reserve to protect the endemic vegetation around the crater, as well as the crustaceans and birds who have made the islet their home.