Lenin's Mausoleum in the Moscow Krelim
Red Square, Moscow. The easiest way to identify this is by knowing that a kremlin is a fortress, and not a building. (There are kremlins in several other cities as well.) It has walls and there are buildings inside, specifically churches, governmental buildings, and museums. In order to enter, you need to get a ticket for a specific exhibition for a specific time outside the walls. It is open to the public 10:00-6:00 on all days except Thursday, with the last time slots ending at 5 or earlier. I got to the ticket office at 4:30, so was unable to enter, but I do have many photos from outside of the walls.