Geysir and Gullfoss are the two classical destinations of the Golden Circle tour, a day's trip from the capital.
Geysir area has many hot springs. The most famous great Geysir spills up to 100m but erupts irregularly about once a year. Strokkur, a slightly smaller geysir in the vicinity, produces eruptions up to 20m every ten minutes or so.
geysir : Gullfoss, a bit closer