Västergarn flourished in the Middle Ages as a significant trading port, second on Gotland only to Visby. Plans were laid in the mid-1200s to build a large new church here, but after the farmers of Gotland were defeated by the burghers of Visby in the civil war of 1288, the funds and ambition to finish the project disappeared. Only the chancel was ever built, and it is this modest, almost square structure that survives today as the parish church—reputedly the smallest medieval church on Gotland.
Traces of the abandoned scheme can still be read in the building. A blocked round-arched doorway in the west wall is thought to have been intended as the triumphal arch leading into the never-built nave. Later, in the late 1200s, the windows were altered and the original chancel arch was walled up as the building was adapted to serve as a stand-alone church. A steep saddleback roof, topped with a small ridge turret, gives the exterior its distinctive silhouette; the church has no tower.
Inside, the space is covered by an eight-part tent vault. The thicker northern wall conceals a built-in staircase and a narrow eastern chamber used as a sacristy. Sources differ slightly on the character of some features, but the overall impression is of a compact, sturdy stone chancel adapted for parish use over the centuries.
The church did not stand alone. Immediately northwest is the grass-grown ruin of an earlier Romanesque church, an apsidal building dated to the mid-1100s and, according to archaeological investigation, the largest Romanesque stone church on Gotland outside Visby. Remarkably, it remained in use alongside the newer chancel and was not abandoned until the 1500s. Northeast of the church lie the remains of a medieval defensive tower, a kastal, probably built in the 1100s and linked to Västergarn's surviving semicircular rampart, itself a reminder of the settlement's former importance as a fortified harbour.
Among the furnishings noted by sources are a sandstone font dated 1592 and a sandstone altarpiece of 1641 depicting the sacrifice of Abraham, decorated with royal and noble insignia reflecting Danish overlordship of Gotland at the time. Older medieval carvings once belonging to the church, including a Gothic Virgin and fragments of an earlier altarpiece, have since been moved to the Gotland museum in Visby. The church also has a small mechanical organ built in 1857 by a self-taught local craftsman, later restored in the twentieth century.