
I am not a big fan of Zoos but as they go, Berlin Zoo is quite spacious so wear comfortable shoes!
If you have the time, do make a trip to Potsdam and visit Sancoussi (
http://www.germanplaces.com/germany/sanssouci-potsdam-sights.html) - it's real beautiful and steeped in history!
The Nature Museum is brilliant as well so is the Egyptian Museum!
Shopping is very cheap as well ;).