The Park Inn by Radisson Berlin Alexanderplatz is the tallest building and the eleventh-tallest structure in Berlin and the 29th-tallest building and tallest hotel-only building in Germany. The 37-floor skyscraper is in the northeast of Alexanderplatz in the central Mitte district and has a height of 125 metres (410 feet).

The complex was built from 1967 to 1970 in the course of the redevelopment of Alexanderplatz when it was located in East Berlin. It was designed by the team of Roland Korn, Heinz Scharlipp and Hans Erich Bogatzky. However, the design as built differs in the shape and location of the tower on the lot from that envisaged in the 1964 plan for redevelopment of the square. The hotel opened as the Hotel Stadt Berlin, part of East Germany’s Interhotel chain. It was a four-star hotel and mainly served for the accommodation of Comecon representatives. There was a panorama restaurant on the 37th floor and unusually fast elevators for the time and place.

In 1993, after German reunification, it was renamed Forum Hotel Berlin. In 2003, Rezidor Hotel Group became the operator of the hotel, which was renamed to Park Inn Berlin-Alexanderplatz[2] and then Park Inn by Radisson Berlin Alexanderplatz. 

There is a public viewing platform on the roof. All the rooms were refurbished starting in 2001 at a cost of € 20 million. Between May and November 2005 the entire 15,000-square-metre (160,000 sq ft) façade was replaced; the 6,800 new mirror-glass panes cost €3 million. In October 2006, two 35-metre (115 ft) antenna masts were erected on the roof, bringing the total height of the building to 149.5 m (490 ft).
Source: Wikipedia