The monastic site at Ardmore is situated on a hillside overlooking Ardmore Bay. Structures associated with the monastery on the site are St Declan's 'House', a small, single cell structure with antae, now much restored; the 12thc. round tower; and the cathedral. The cathedral comprises nave (22.1 m x 7.95 m internally) and chancel (10.6 m x 5.8 m internally) and represents at least four different phases of building. Romanesque work surviving in the building includes the N doorway; five windows in the nave; string courses and blind arcades in the nave; the chancel arch; and most famously, the figurative friezes set in the western gable.

The early monastery here was founded by St Declan, who was reputed to have been bishop of Munster prior to the arrival of St Patrick. Two Ogham stones, now preserved in the cathedral, are all that remains of this earliest phase of Christian occupation. Ardmore was certainly a bishopric by 1172 when a bishop from Ardmore did fealty to Henry II. Eugenius bishop of Ardmore witnessed a charter issued by Diarmuit MacCarthaig in favour of the church of St John in Cork c.1172-9. In 1203 the Annals of Inishfallen record that 'Mael Etain Ua Duib Ratha, the noble Priest who completed the building of the church at Ardmore, died'. There is no record of the diocese after this date. In 1591 Ardmore was leased to Sir Walter Raleigh for two years, and in 1642 the Confederate army hiding in the church and round tower were besieged by the English and hung on the spot. The site is currently in the care of the National Monuments Service.

The cathedral incorporates at least 4 phases of construction. The earliest phase appears to the E of the chancel arch where walls with evenly coursed, well-finished masonry indicate the presence of a 10th-11thc. single cell building. This building appears to have been expanded westwards at some period during the mid to late 12thc., as evidenced by the fragmentary remains of multi-scallop capitals incorporated into the chancel arch. Extensive additions were made to the church probably in the very late 12thc. or early 13thc. This included the reconstruction of the chancel arch in its present form, the nave windows, the window currently in the W wall and the doorway currently in the N wall. The friezes currently on the exterior of the W wall may also belong to this period. During the 17thc. (as indicated by a date stone in the NW buttress) the building underwent extensive renovations. Buttresses were inserted against the W face of the chancel and the entire W end was rebuilt, again incorporating features from earlier phases of building The figure sculpture at Ardmore is the only surviving programme of 12thc. figure sculpture in Ireland, although fragments at Freshford, Ullard and Liathmore imply that this form of sculpture may have been more common than the remaining evidence suggests. The doorway may be compared with that from Inislonaught Co. Tipperary, now at Marlfield.