Hamburg's most famous (or should that be infamous?) street!
Known locally as the 'Kiez' the Reeperbahn is the centre of Hamburg's nightlife. Here you will find restaurants, clubs and bars and perhaps more famously strip joints, sex shops and the sex museum! Although there are seedy parts, much of it is mainstream and it's certainly where all manner of tourists and locals alike will go out whatever night of the week it happens to be.
Popular places to head for are the Hans-Albers Platz off the Reeperbahn and Grosse Freiheit just on the north side. Both have plenty of good bars and clubs to choose from and are safe areas to wander. Avoid Herbertstraße unless you are looking to visit a prostitute. This is a closed-off street (juveniles and women aren't allowed!) where prostitutes wait behind lit windows for prospective customers.