The castle, possibly built by the O’Connors in the 14th or 15th century, sits atop high ground with commanding views across the Offaly countryside; from here you can see Croghan Hill 4.1 kilometres to the west and the extensive boglands of Coole stretching to the south. What makes this site particularly fascinating is how the medieval structure was reimagined in the mid-18th century, when the surrounding land was raised to create formal gardens for Toberdaly House, effectively transforming the old tower into a corner feature of the new estate’s 46-metre by 35-metre walled garden.

The tower house itself stands three storeys high, built from random rubble with dressed alternating quoin stones, its walls showing a slight base batter typical of medieval defensive architecture. A section of wall running approximately 29 metres east from the tower’s southeastern angle may be a surviving fragment of the original medieval bawn wall; the lack of a visible straight joint where it meets the tower suggests these structures were built together. When Toberdaly House was constructed 24 metres to the northeast in the 18th century, the castle underwent a remarkable transformation: an octagonal gazebo was added to its top whilst the interior was converted into a dovecote, giving this military structure an unexpectedly genteel second life.

Historical records provide tantalising glimpses of the castle’s earlier incarnation. A 1550 survey of O’Connor lands described Toberdaly Castle as ‘an old ruynouse base courte whereof a greate parte of the wallys standeth’ in the Lordship of Tuath Maigh Clann Colgain. The term ‘base courte’ might refer to a bawn or curtain wall of an enclosure castle rather than a tower house, though certainty remains elusive. Today, ivy obscures much of the western wall that runs from the tower’s northwestern angle, making it difficult to determine which sections date from the medieval period and which from the 18th-century renovations, leaving visitors to puzzle over where one era ends and another begins.