The Wonderful Barn, Folly in Leixlip, County Kildare, Ireland

The Wonderful Barn is a tall, tapering conical stone tower on the Castletown House Estate, its lower courses of rough light stone broken by projecting bands. An external stone staircase spirals up to a small cylindrical top stage with a shallow conical roof, and two small triangular openings sit one above the other on its face. A small stone building with a pitched slate roof adjoins the base.

This structure was built in 1743 as a grain store and work project during a major food shortage affecting the region. It demonstrates how wealthy landowners of the era used building projects to provide employment during hardship.

The Irish name is An Iothlainn Aisteach. Doves were a Georgian delicacy when game was out of season, which is one suggested use; the tower's height also suited shooting or a gamekeeper's lookout. It stands on the Leixlip side of the former Conolly estate, and a similar tower, the Bottle Tower, was later built at Churchtown near Rathfarnham.

The building stands on private estate grounds and can be seen from outside but is not open to visitors to enter. It is most visible from the approach road that leads toward the main house.

The barn was built in 1743, just after the famine of 1740–41, and its central hole through each floor points to its likely use as a granary. A similar structure, the Bottle Tower in Churchtown near Rathfarnham, was built in imitation of it.