At the place where the Kamenický stream meets the Sázava river, you can visit the mysterious ruins of the royal castle demolished Kostelec. The ruins are part of a nature reserve and are freely accessible.
The castle was probably founded in the last third of the 13th century by King Wenceslas II, but the first written mention dates back to 1342, when it was held in pawn by Oldřich Medek of Valdek. Although Charles IV bought back the castle in 1356, he soon pawned it again and it had several owners over time. The last of them was Kuneš Rozkoš of Dubá from 1443, who looted in the surrounding area, and therefore the castle was besieged in 1449. It withstood this siege, but a year later, on May 18, 1450, it was besieged again and five days later it was conquered by the army under the command of Zdeněk Konopišťský of Šternberk, who became its new owner. In 1456, serfdom was abolished and he fortified it as one of his military strongholds. Later, he became a leading figure of the anti-Poděbrady opposition, and therefore the royal army captured and destroyed the castle in 1467.
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.