Potsdam has many more historical landmarks. The Dutch Quarter is one of the city's most-visited districts, encompassing 150 red-brick houses in Dutch style that were built in the 18th century for Dutch artisans. The Old Market Square is Potsdam's historical city centre. Here you will find the imposing 19th-century St. Nicholas' Church with its classical dome, and the 18th-century Old City Hall. Potsdam also has its own Brandenburg Gate, just like its bigger neighbour Berlin. It forms part of the original city wall and is one of three gates still standing. A final tip for visitors is the Einstein Tower is the Albert Einstein Science Park, which is still a working solar observatory.