In 1680 the first Duke of Ormond had a waterhouse and banqueting hall constructed beside the castle's bowling green, a structure that combined working infrastructure with something close to theatrical luxury. It was gone within a century, vanished before John Rocque completed his survey of 1758, leaving almost no physical trace.

The travel writer Thomas Dineley visited in 1681 and recorded what he found in vivid, unhurried prose. The waterhouse served a practical function: a horse-powered engine drew water and supplied the castle's domestic offices. But attached to this working machinery was a summer banqueting room, the term referring in this period not to a dining hall in the modern sense but to a small, often ornamental pleasure room used for sweetmeats and conversation after a formal meal. Dineley described it as floored and lined with black and white marble, its ceiling painted with angels against a sky, and at its centre a fountain of black marble shaped like a large cup. A jet of water rose from the middle of this fountain, climbed into the hollow of a carved ducal crown suspended above it, and fell back down through several dripping points around the rim. A letter recorded among the Ormond manuscripts captures something of the ambition involved: the marble piers beside the grotto could not be moved across the bowling green until dry weather permitted, and the writer concluded that "the like were not seen in this kingdom heretofore." Dineley himself sketched the exterior, showing a circular turret capped with a statue, an image repeated in Francis Place's 1699 view and Henry Pratt's of 1708.

What survives today is the description rather than the structure itself. The site lies approximately seventy metres north-east of the castle's north-east wing, in an area now covered by trees. For anyone familiar with the castle grounds, it is worth pausing at that wooded margin and considering what once occupied it: a horse turning an engine, water rising through a marble crown, and painted angels overhead.