In my opinion the best way to visit Berlin is riding a bike. There are several places to rent a bike but I recommend you to call Alex. They have a shop next to the U-Bahn Station of Weinmeisterstrasse in Mitte and they also organize bike tours. We call them and within 20' a charming young man came carrying the bikes for us.
Alte Schönhauser Straße
U-Bahn Station Weinmeisterstrasse
T. +49 (0) 176 670 92 856