Bremen is a port city in northern Germany located along the Weser River with a population of approximately 545,983 people. Many of the sights in Bremen are found in the old town, an area surrounded former moats of the Medieval city walls. The oldest part is in the southeast section. Interesting buildings in the vicinity of the marketplace include a 16th-century guild hall, and the former weighing house. On one side, there are museums, art galleries, universities and colleges, parks and rivers, the Beck's Beer Tour, and the Space Center. On the other side of the Weser River, Bremen is famous for a fairy tale by the Brothers Grimm, the Town Musicians of Bremen. Every year, Bremen hosts a Free market, one of the world's oldest and continuously celebrated fairground festivals. Bremen is also host to one of the four big annual techno events, one of which is the Vision Parade.