There are three main structures at Brocken summit. The building to the left is the Brockenherberge, a hotel with two restaurants, and also a climate reference station, although it was once a weather station. The red and white tower in the middle is an FM radio and television transmitter antenna built in 1973. There are several microwave dishes on the three lower rings. To the right is Brockenhaus, the information center for the Harz National Park. This building was once known as the Stasi-Mosque, a surveillance installation of the GDR Ministry for State Security. The Stasi have been described as one of the most effective and repressive intelligence and secret police agencies in the world.