Despite its name, the original purpose of this building is uncertain, although there are subterranean archways into which boats could have been floated.
There is also a small platform with steps to the gardens. At one time a floor was introduced halfway up, and windows added, forming a small apartment reached by a narrow staircase on the eastern side. This quite attractive structure with its slate roof was, however, reduced to a shell by a fire in 1968.
