This is the abandoned Radrennbahn (Velodrome) in Hannover; first opened in 1965. This track saw many races over the years as shown by the posters in the basement. The city of Hannover cut funding for this facility. It's last race happened in September of 2017 and has not seen one since. I have doubts of this place re-opening due to the damage to the buildings and the track. When the track closed they had cut parts of the track to prevent people from riding their bikes on it.
Please exercise caution when in this building. There is a lot of mold, water and live electricity going to this building. There is also part of the building where you could easy become trapped. There is a lot of broken glass that could easily go through your shoes and random pieces of metal hanging from the ceiling that could cut you.