The monument consists of the extensive remains of a monastery originating in the pre-Norse period. The site is clearly very complex with a long building history but has never been excavated which makes the interrelationship between features difficult to assess.
The core of the site is a precinct on fairly flat ground which contains two church structures (one of stone and clay construction) a subterranean chamber and several other structures whose function and original form are thought to derive from the ancillary buildings needed for a small monastery. To the east is a substantial burial ground with graves formed as raised rectangular platforms.
To the east of this site are a pair of interconnecting bee-hive cells which are thought to be the oldest structures on the island. The highest part of this structure still stands to over 3.5m high.
There are numerous other structures between the core of the site and the natural boat-landing to the south: for example, cross bases and terracing, apparently designed to monumentalise the approach to the monastery.
To the SW of the core of the site an Early-Christian burial cairn, (known as Eithne's grave) with a cross-marked slab, occupies a natural terrace on the hill side. There is a second burial ground roughly 200m to the SW of the main site.
In addition to the features noted above, there are several features and remains which relate to post-medieval farming on the island, in particular a well preserved corn-drying kiln to the N of the site core, a barn, several alterations of the monastic remains and areas of rig and furrow.
The site is first recorded by John of Fordun who described it as a sanctuary. The site is clearly older than this but is thought to have been in virtually continuous use since its foundation in the Early Christian period. It is now thought that the site is likely to have been founded by St. Brendan the Navigator.
The area to be scheduled includes all the features noted above. It is defined to the SE by the high water mark and to the NW by the edge of the cliffs which run up the NW side of the island. To the NE and SW the area is defined by two lines running NW-SE.
The first runs 50m SW of the SW burial ground and the second 70m NE of the corn kiln. The area measures 510m from its northernmost to its southernmost point by 490m from its easternmost to its westernmost point and is marked in red on the accompanying map.