The structure, likely dating from the late medieval period, was built using substantial limestone blocks quarried from the surrounding landscape. What remains today are the ghostly outlines of what was once a formidable fortified residence, with its eastern wall still standing at 11.3 metres in length and rising three courses high, featuring the characteristic base batter that helped deflect projectiles and strengthen the foundation.

The tower house's footprint reveals a rectangular plan, with portions of the southern and northern walls still visible, each measuring approximately 11 metres long and 1.5 metres thick; substantial dimensions that speak to its defensive purpose. The western wall has completely vanished, whilst significant collapse is evident at both the southeastern and northeastern corners, where time and weather have taken their toll on the masonry. These ruins were first formally documented during the Irish Tourist Association Survey in 1942, though local knowledge of the site stretches back much further.

Tower houses like Cashlan Brock were the preferred dwelling of the Gaelic and Anglo-Norman gentry from the 15th to 17th centuries, serving as both home and fortress during turbulent times. Their elevated positions, as seen here, provided strategic advantages for surveillance and defence whilst also asserting the owner's status in the landscape. Though now reduced to weathered walls and tumbled stones, these remains continue to mark an important chapter in Offaly's architectural heritage, standing as a testament to the county's medieval past.