Rostov’s impressive Kremlin was built in the 17th century under the orders of the powerful Metropolitan Iona of Rostov. He wanted the town (which in those days still wielded some power in the region) to have one of the most beautiful Kremlins in the country and to that end he dug deep into the church's coffers to build this imposing fortress.
Nowadays within the Kremlin walls there are numerous museums, although unfortunately most of them are of little interest to foreign visitors. It is however well worth climbing up the Kremlin walls and the bell tower, taking a look in the cathedral and checking out the regular art exhibitions.
In front of the Kremlin is the huge 12th century Dormition of Mary Cathedral, which is in essence a working church - although it should be noted that inside it is undergoing a complete renovation. For a small extra fee you can also climb up the adjacent bell tower for a view over the surrounding area.
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.