Grot (grotto) is probably the most mystical of the Valley geysers. Its vent is located on the Vitrazh ledge, on the right, in a small cave wrapped in clouds of steam. Stories about its eruptions were considered a myth for a long time, until several eruptions were photographed and filmed in 1991. Since then quite a few people witnessed it and Grot is commonly considered to be a geyser with infrequent eruptions that happen on irregular schedule.
Grot eruption is a grand spectacle. Angled, almost horizontal jet of boiling water shoots across Vitrazh with massive roar, washing away clay and geyserite on its opposite end. 60 meters jet and eruption volume of several dozens of cubic meters make Grot the biggest geyser in the Valley. However, only a few lucky people can witness the eruption.
One interesting characteristic of Grot geyser is that it erupts in series. There are 7—9 eruptions in a row, 2—3 minutes each, with pauses of the same length in between. After that it quiets down for an uncertainly long time. It's suggested that Grot's eruptions are caused by specific conditions, when water level at the bottom of the cave falls especially low.