English: Artemisia Geyser is a large, regularly-erupting geyser in the Cascade Group of Yellowstone's Upper Geyser Basin. It erupts approximately once a day for about 15 to 30 minutes. The geyser has a beautiful, blue water-filled, hexaradiate basin that is about 12 to 16 meters across. The vent is surrounded by a large platform with complexly anastomosing ridges of nodulose geyserite. Eruption water drains to the southeast toward the Firehole River along numerous individual runoff channels. Eruptions start with subterranean thumping and a sudden flooding of the geyserite platform with increased runoff. Eruptive bursting starts with small doming roils that increase significantly in size and energy as the eruption progresses. Eruptions end gradually. Some water from the platform drains back into the vent after the eruption and water level settles down to about 1 meter below the rim. Water slowly fills up the basin over many, many hours after the eruption, eventually reaching overflow. This continues for many more hours until the next eruption.

In 1999, researchers measured the vent's water temperature as 80 degrees Celsius, with a pH of about 7.7 (= slightly alkaline).

In early August 2016, a Yellowstone ranger witnessed an act of significant vandalism to this geyser by nature-hating scum.