There are the remains of an Irish round tower on the edge of the Armoy village. An early monastery was founded about AD 460 by Saint Olcán, a disciple of Saint Patrick. The only trace of an early monastery is the stump of the round tower, which stands in the grounds of St Patrick's Parish Church. The tower is about 11 m high and has three storeys. At one time, Armoy was the main religious settlement in the Irish part of the kingdom of Dál Riata.
Visby Cathedral (also known as St. Mary’s Church) is the only survived medieval church in Visby. It was originally built for German merchants and inaugurated in 1225. Around the year 1350 the church was enlarged and converted into a basilica. The two-storey magazine was also added then above the nave as a warehouse for merchants.
Following the Reformation, the church was transformed into a parish church for the town of Visby. All other churches were abandoned. Shortly after the Reformation, in 1572, Gotland was made into its own Diocese, and the church designated its cathedral.
There is not much left of the original interior. The font is made of local red marble in the 13th century. The pulpit was made in Lübeck in 1684. There are 400 graves under the church floor.