Block 5 was loaded with fuel and briefly went critical but it never went online. Block 6 was built and about a year from being loaded with fuel when the Berlin Wall fell and the plant was shut down pending a refit to meet Western safety standards (which blocks 1 through 4 didn't meet). Eventually it was decided to decomission the whole plant. Since Block 6 was never loaded with fuel it holds no radiological hazards whatsoever and is now a museum with a free guided tour. I recently had the opportunity to take that tour. So without further ado here's pictures from inside a nuclear reactor: