Clopook derives from the Irish Cloch-an-Phuca, the stone or stone fortress of the pooka, that shapeshifting spirit of Irish folklore. An alternative reading recorded in the History of Queen's County renders it as Dun-Cluain-Phuc, "the fortress of the lonely spirit". Either way, the place carries an older unease than its archaeology alone can account for. Perched on a prominent limestone rock outcrop in Co. Laois, rising more than 42 metres above the surrounding land, the Dun of Clopook is a large polygonal enclosure roughly 100 metres across, its summit defended by a bank of earth and stone and, on the eastern side, a surviving stone wall. Beneath the fortification, cut into the south-western face of the rock, is a substantial cave, described in 1852 by Daniel Byrne as running nearly 12 metres in from its entrance before narrowing sharply and being closed off with dry stone, placed there to prevent cattle from wandering in and becoming lost.

Byrne considered it likely that the site had served as one of the chief fortresses of the O'Moore clan, perhaps even a royal residence, at a very early period. The placename appears on a 1563 map of Laois-Offaly, and the fort sits within what was then the Gaelic lordship of Farryn O'Kalle. As Gaelic power in the midlands was broken and plantation took hold, the lands changed hands repeatedly through Crown leases: to Sir John Travers in 1551, to Francis Cosby in 1569, and to Alex Cosby of Stradbally in 1593. By the time the 1906 Ordnance Survey map was drawn, the summit still showed a causewayed entrance across a rock-cut fosse on the west, a second entrance gap on the east with a small outer bank functioning as a barbican, and the remains of what appeared to be a small tower house in the south-eastern interior. The 1838 map shows none of those buildings, which raises questions about when they were built or when they disappeared. A cave features on both maps, and a circular pond of unknown antiquity sits at the base of the slope to the south-south-west.

The interior of the monument is now effectively invisible. Dense woodland and thick undergrowth cover the hillfort entirely, making it impossible to examine the enclosing bank or the remains within at ground level. The site lies about two miles south of Timahoe, and its summit, at 186 metres above sea level, would in clearer conditions offer views across a wide stretch of the Laois countryside, towards the Dun of Luggacurren less than a kilometre to the south, and towards a standing stone to the east.