A bizarrely shaped famine-era folly which has been separated from the grounds of the the nearby Castletown Estate. See also Connolly's Folly.
Castletown Estate houses a palladian mansion that was home to the Speaker William Connolly and his wife, Lady Louisa, who it seems commissioned the follies, some of which, including the Wonderful Barn and Connolly's Folly, were never or are no longer part of the remaining Estate.
At the site of the Wonderful Barn near Leixlip, a short loop can be undertaken of the surrounding fields but in truth it's nothing to write home about due to the dampness of the fields and the road noise.
Worth a quick visit if you're local or interested in follies. Can sometimes be seen from the N4.