Geysir (sometimes known as The Great Geysir), in the Haukadalur valley, Iceland, is the first geyser ever described in a printed source and the earliest geyser known to Europeans. The English word geyser (a spouting hot spring) derives from Geysir. The name Geysir itself is derived from the Icelandic verb geysa, "to gush", the verb from Old Norse. Geysir lies on the slopes of Laugarfjall hill at , which is also the home to Strokkur geyser about 50 metres south.
Eruptions at Geysir can hurl boiling water up to 70 meters in the air. However, eruptions may be infrequent, and have in the past stopped altogether for years at a time.