I very much stumbled on this place in the dark during the Hanze696 audax. I didn't realise there were any such sites so far west - but why wouldn't there be? - so I didn't connect going to "Bergen" with "Bergen-Belsen".
Everything was shut when I got there (10pm?), riding along a quiet woody A-road. But a lady was manning a desk in the visitors building; she gave me a funny look, and by the time I left there was a burly security guy hovering next to her.
A very sobering experience.