The effect is less country house than stage-set castle, and that is more or less the point.

The original structure dates to the early eighteenth century, but it was William Tonson who gave Lisnagar its current character when he enlarged and remodelled it in the early nineteenth century. The style he chose was Tudor-Gothic, a fashionable mode of the period that borrowed the pointed arches, battlements, and decorative stonework of late medieval England and applied them to houses that were, underneath the theatrical dressing, entirely domestic in function. The result at Lisnagar is T-shaped in plan, with a slightly taller extension to the east echoing the design of the main front, its own projecting bow adding to the layered, asymmetric quality of the whole composition. The curtain wall, a low defensive-looking boundary normally associated with castle enclosures, here serves a purely ornamental purpose, tying the house to its farm range in a single composed landscape gesture. A large ornamental lake to the east completes the picture, suggesting that Tonson was thinking not just about the building but about how it would sit within its grounds as a designed whole.