The historic centre of Berlin is surprisingly compact and is best explored on foot. It's safe to walk anywhere in the central city, including in the large parks like Tiergarten, though as in any city, be extra careful at night.
When Berliners have to be somewhere else, they're most likely to walk, or use public transport or bicycles to get there. In fact, many of them don't even own a car and those that do, don't use it for every single trip. So when in Berlin, do as Berliners: it's smarter, cheaper and saves you from looking for that elusive parking spot. Berlin's extensive and efficient public-transport system is operated by BVG and consists of the U-Bahn (underground, subway), S-Bahn (light rail), buses and trams.
Buses run frequently between 04:30 and 00:30. From Sunday through Thursday, night buses take over in the interim, running roughly every 30 minutes. Buses N2, N5, N6, N8 and N9 follow more or less the routes of the U2, U5, U6, U8 and U9. Night buses don't run on Friday and Saturday night, when U-Bahn service is available 24/7.
The rickety trams of Berlin's past have been replaced with sleek new versions. They operate only in the eastern sections of the city; about 30 lines crisscross the entire eastern half of Berlin. The M10, N54, N55, N92 and N93 offer continuous service nightly.
You'll find taxi ranks at the airports, major train stations and throughout the city. Taxis can also be ordered by telephone but they are cheaper if flagged down. There should be no surcharges for night trips; bulky luggage costs extra. For short trips, you can use the Kurzstreckentarif (short-trip rate), which entitles you to ride for up to 2km. It is only available if you flag down a moving taxi and request this special rate (3.00) before the driver has activated the regular meter. If you continue past 2km, regular rates apply to the entire trip. In the inner city there are also some two-seater pedicabs, assisted with electric engines, called Velotaxis, although they're mostly used by footsore tourists.
Bike lanes abound in flat Berlin. Bicycles (Fahrräder) may be taken aboard designated U-Bahn and S-Bahn cars (though not on buses) for the price of a reduced single ticket.