The island sits in Portmagee Channel, roughly 120 metres off the shore and about 400 metres west-northwest of Portmagee village. Its entire habitable surface measures no more than 26 metres by 50 metres, just under a tenth of a hectare, yet packed into that small patch of ground are the remains of an oratory, a corbelled stone hut, a gable-shrine, a leacht, and a spring-fed well, all enclosed within the curve of a monastic cashel wall. A cashel is a dry-stone enclosure wall defining a monastic or ecclesiastical precinct, a form common in early medieval Ireland. On the western side of the island, roughly fifty upright stone slabs stand in what appear to be regular rows, and Ordnance Survey records describe the island as a burial place for children and for adult strangers, suggesting the slabs mark graves of those who could not be interred in consecrated ground elsewhere.

Four seasons of archaeological excavation between 1992 and 1995 uncovered about seventy per cent of the island and clarified a long sequence of use. The stone oratory near the eastern edge, whose walls of horizontally laid slabs are preserved to a height of around 0.45 metres, dates to at least the seventh or eighth century; a radiocarbon date of 640 to 790 AD came from a layer overlying its clay floor, and beneath it lay traces of two earlier sod-built structures. The leacht, a type of raised rectangular platform associated with early Christian commemoration of the dead, was found to underlie the oratory on its northern side and to support a gable-shrine on its upper surface. The gable-shrine itself, made from two slate slabs with semicircular notches cut into their upper edges, covered two small cists containing exhumed human bones, scallop shells, and quartz pebbles. Nearby, the corbelled circular hut near the southwest end of the island, with walls up to 1.8 metres thick and tall, had its floor set below the surrounding ground level. A midden deposit beside it, consisting of shells, bones, and charcoal, produced an eleventh-century radiocarbon date and yielded fragments of an antler comb, bone beads, and two bronze ring-brooches. Beneath the midden was evidence of an even earlier circular timber structure. The island has no historical documentation, and even its name is uncertain: Lochán may refer to a saint, possibly one of two figures named Lochán recorded in the Martyrology of Oengus compiled around AD 800, or the name may simply mean the island of the chaff.

The stone-lined well, roofed with a large lintel and reached by five descending steps, sits midway between the oratory and the hut. It was mistakenly identified as a souterrain, an underground passage sometimes used for storage or refuge, by the scholar Françoise Henry in 1957; excavation confirmed it is in fact a well, apparently spring-fed. The island is accessible on foot from the mainland only during certain low tides, so any visit requires attention to the tidal conditions along Portmagee Channel.