Grábrók is a volcanic crater located in West Iceland, near Lake Hreðavatn. Formed around 3,400 years ago, it's the largest of three craters in the area. The lava from its last eruption dammed the river Norðurá and created Lake Hreðavatn. Grábrók is a popular hiking spot with easy trails for all ages, offering scenic views over the university campus and moss-covered lava fields of Borgarfjörður. Don't forget to check out the nearby roadside restaurant, Hreðavatnsskáli, for a bite to eat after your hike!