The Secret Lagoon, also known as Gamla Laugin, is Iceland's oldest natural swimming pool located near Flúðir. It was built in 1891 and is fed by geothermal hot springs like Vaðmálahver and Básahver, maintaining a cozy temperature of 38-40 degrees Celsius year-round. The pool's rich history includes being used for bathing, washing clothes, and even hosting the Flúðir community's legislative body. After years of neglect, it was revitalized in 2005 and reopened in 2014, offering visitors a relaxing and authentic Icelandic experience surrounded by stunning geothermal features.