Stralsund is one of the oldest cities in northeastern Germany, founded by the Danes in the early 9th century. The city is located at the southern end of the Strelasund, a sound that separates the island of Rügen from the mainland. The Rügen Bridge, a 12-km (7.5-mi) long bridge, connects Stralsund with the island. The old city is a UNESCO World Heritage Site. It is dominated by a series of Gothic churches, the most notable of which is the Marienkirche, built in the 13th century. Other notable landmarks include the Rathaus (city hall), also built in the 13th century, and the Stralsund Museum, housed in a former Dominican monastery.