Grettislaug is a geothermal hot pool in Skagafjordur, close to the town of Saudarkrokur. The pool is named after Grettir Asmundarson, a famous outlaw written about in the Icelandic Sagas. Also known as Grettir the Strong, he is considered the strongest man in the sagas. His story is detailed in the Grettla, the Grettis Saga.

According to the story, Grettir made his home on Drangey Island, an isolated rocky outcrop that is visible from the pool. He swam ashore and would use the waters of the geothermal pool to warm himself.

The pools have existed for a long time but in the early 1930s after a big storm, they were both destroyed. It wasn't until 1992 that a local farmer, Jón Eiriksson, had the initiative to rebuild the pool and called it Grettislaug, the water temperature is about 39-42 degrees Celsius.