An underground chamber built as a folly. These could utilise a cliff edge of exposed rock, or be a construction above the level of the ground - but pretending to be below it, by using large stones. These were common in the mid-18th century. At Hartburn (Northumberland), niches were carved and a 'house' frontage erected at the base of a cliff. It is thought that Archdeacon Sharp was responsible for this in the 1760s AD. Other grottos are noted at Bebside Hall and Great Bavington Hall, (both Northumberland). That for Great Bavington Hall is illustrated and marked on Armstrong's 1769 map of Northumberland. These would have statues of Classical gods or depictions of the Arts, perhaps in niches.