Geysir (The Great Geysir) is a geyser in southwestern Iceland. The name Geysir itself is derived from the Icelandic verb geysa ("to gush") the verb from Old Norse. Geysir lies in the Haukadalur valley on the slopes of Laugarfjall hill, which is also the home to Strokkur geyser.
Eruptions at Geysir can hurl boiling water up to 70 metres (230 ft) in the air. However, eruptions may be infrequent, and have in the past stopped altogether for years at a time.
The nearby geyser Strokkur erupts much more frequently than Geysir, erupting to heights of up to 30 metres (98 ft) every few minutes. Strokkur's activity has also been affected by earthquakes, although to a lesser extent than the Great Geysir. Due to its eruption frequency, online photos and videos of Strokkur are regularly mislabelled as depicting Geysir. There are around thirty much smaller geysers and hot pools in the area, including one called Litli Geysir ('Little Geysir').
Descriptions of the Great Geysir and Strokkur have been given in many travel guides to Iceland published from the 18th century onwards. Together with Þingvellir and the Gullfoss waterfall, they are part of the Golden Circle that make up the most famous tourist route in the country.