Hässelby Castle (Hässelby slott) was built first in the 1640s by the riksråd Karl Bonde, who owned it until his death 1652. The original architect was Simon de la Vallée and the castle was finished about the 1660s by his son Jean de la Vallée, when Karl's son Gustaf Bonde owned it. The Bonde noble family owned the castle until 1931, when Stockholms stad bought it until 2010. Since 2010 SIVAB own the castle. Today Hässelby is opened for weddings, parties and conferences.
References: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.