I lived in east Berlin for over a year back in 96..still one of my fav Cities of all time..Loads to do if you want.
If you like abit of shopping, vist the KeDaWe store on the Kudam..better than Harrods. The Food Hall on the top floor is worth the visit on its own !!
Berlin Zoo is well worth a look. So is the Sealife Centre (take the trip Up inside the Huge Aquarium)
The museum at Checkpoint Charlie is very interesting.
And if you fancy a pint pay a visit to the Irish Bar in the Europa Centre and next door to that is a great Bavarian Restaurant that serves great food.
Hope you have a great time…we always do when we go.
Bush.