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:Celje Castle was once the largest fortification on Slovenian territory. The first fortified building on the site (a Romanesque palace) was built in the first half of the 13th century by the Counts of Heunburg from Carinthia on the stony outcrop on the western side of the ridge where the castle stands. It had five sides, or four plus the southern side, which was a natural defence. The first written records of the castle date back to between 1125 and 1137; it was probably built by Count Gunter. In the western section of the castle, there was a building with several floors. Remains of the walls of this palatium have survived. In the eastern section, there was an enclosed courtyard with large water reservoirs. The eastern wall, which protects the castle from its most exposed side, was around three metres thicker than the rest of the curtain wall. The wall was topped with a parapet and protected walkway.