The Aragonese Alfonsino Castle, best known as Forte a Mare ('Sea Fort'), was built by King Ferdinand I of Naples in 1491 on the S. Andrea island facing the port of Brindisi. It is divided into two sections: the 'Red Castle' (from the color of its bricks) and the more recent Fort.
The castle was besieged by Venetians in 1529 and French army in 1799. It was damaged by storm in the modern age and was abandoned in 1984.
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.