Geysir is a famous hot spring in Iceland's Haukadalur Valley, known for its geysers and hot springs. While Geysir itself doesn't erupt much these days, nearby Strokkur puts on a show every 5-10 minutes, shooting water up to 130 feet high. The area also has bubbling mud pots and fumaroles emitting steam. Visitors can explore the valley, relax in natural pools like Kualaug, and check out the Tree Museum.