Newly opened in May 2005, the Holocaust Memorial to the Murdered Jews of Europe occupies a vast site immediately south of the Brandenburg Gate. It's made up of more than 2,700 giant concrete slabs. Don't hop on them: it annoys the guards. The underground information centre is very good and well worth the queue.
Stresemannstraße 90; nearest S-Bahn: Unter den Linden; www.holocaustmahnmal.de
Updates
There are no guards anymore. Wander in and out at your leisure; hop on if you want. The idea is for each person to bring and take to and from the memorial their own personal stuff. I was struck by the number of children enjoying the memorial, whether playing hide and seek between the blocks or just sitting on top playing. As you say, many teenagers do climb on top but I think that this is just as valid a way of interacting with the memorial - I think it is very cleverly designed to have a different impact on different people. You can take it lightly or seriously as you wish.
Is this your business?