What I am looking for/to research is a memorial my students went to (I think they said they had visited it in Germany, I want to say it was Berlin but I'm not sure)

Essentially, it's commemorating the war, and it's a tunnel/hall that you're suppose to enter and it's not all it seems when you enter it, It's meant to remind you to be perceptive with other people. It seems like something memorable, as they were merely visiting and it stayed in their minds.

I am so sorry that I don't have more details, they told me about it a while ago and I had just reminded myself of it. I would really appreciate some help finding this and possibly visiting, wherever it is. Thank you.