As long as it's dry, getting around Berlin is really best done by bicycle. It's a flat city, there are plenty of cycle paths and wide bus lanes for you to use and you see so much more from the saddle than from the U-Bahn train window. Note that cycling on the pavement is illegal and may get you fined, even though everyone does it. Cycling across town may take a while, though for €1,60 you can take your bike on an S/U-Bahn train too. There are dozens of bike rental places, most charging €10-12 per day. The urban bike trip planner www.bbbike.de can suggest low-traffic and cobblestone-free routes across Berlin.