Systrafoss ('sisters' waterfall') is part of the river Fossá, which runs south from its source Systravatn. Both the waterfall and Systravatn take their name from the sisters of the nearby Kirkjubæjar Abbey. Folk tales illustrate history with stories about both good and sinful nuns. The Systrastapi (Sister's rock) is where two nuns of the Abbey were buried after being burned at the stake.
One of the nuns was accused of selling her soul to the Devil, and having carnal knowledge with men. The other was charged with speaking blasphemously of the Pope. After the Reformation, the latter nun was vindicated, and flowers are said to bloom on her grave, but not that of the first nun.