The site of an early monastery, founded in the 7thc by St Mochua mac Lonan. All that remains from the monastic era are remnants of a church, built into a later castle, and the well-preserved round tower. This has a fine Romanesque doorway and retains a conical cap, the latter partially rebuilt in 1880-1. There are four triangular-headed windows at the top, with three further windows at various points lower down. The base is furnished with a plinth with three steps. The masonry varies from sections of well-dressed ashlar to more randomly coursed rubble.

The portal at Timahoe is by far the most elaborate doorway to be found in an Irish round tower and it is unfortunate that lack of access makes it difficult to reach precise conclusions about the sculpture. It can probably be dated between 1150 and 1165 on the basis of the analogies with Killeshin; some of the human masks are exceptionally alike; for example, one head, on the base of the outer order (S side, outer edge) is almost a replica of one of the faces on the outer jambs at Killeshin. Timahoe lacks examples of the Irish-Urnes animal ornament, which, together with greater simplicity of the decoration, might suggest that it preceded the work at Killeshin.

The human mask was a particular favourite of the sculptors at Timahoe: altogether there are fifteen of them. Probably the first examples of this feature in Hiberno-Romanesque carving are those in the nave of Cormac's chapel at Cashel (1127-34).

The combination of human masks and bulbous bases can also be found at Rahan (Offaly), approximately thirty miles away.