The Museum Bunker is a museum at the former headquarters of the local German command during the battle to capture the city at the end of World War 2. The museum presents the city’s 698 years of German past and the Soviet’s “liberation” of the city. This including several interesting dioramas of events during the days of the battle plus some very nicely done recreations of several of the bunker rooms when the German’s were using the bunker.
When you arrive you will find a small yard with only two black upright triangular canopies over the bunker doors and a few pieces of military equipment. Not what you expect until you remember the bunker was underground. In order to find the Museum Bunker go to the first courtyard to the right behind the Kaliningrad Hotel. Other people have said it was difficult to find but Google Maps took me right to it.
The Museum Bunker is, of course, present in Russian, but they do have a lot of information translated into English. I found it to be the most different thing I did in Kaliningrad and am so glad I took the time to visit. It is open daily (except Wednesday) from 10AM to 4PM.