Potsdamer Platz and Kreuzberg

The once-divided capital is rejoined on Potsdamer Platz, which was Berlin's inner-city center and Europe's busiest plaza before World War II. Bombings and the wall system left this area a sprawling, desolate lot, where tourists in West Berlin could climb a wooden platform to peek into East Berlin's death strip. After the Wall fell, Sony, Daimler, Asea Brown Boveri, and other companies made a rush to build their headquarters on this prime real estate. In the mid-1990s Potsdamer Platz became Europe's largest construction site. Today's modern complexes of red sandstone, terra-cotta tiles, steel, and glass have made it a city within a city. The subtle reminder that this was an empty plot for nearly 50 years is a line of cobblestones that traces the path of the Wall on the west side of Stresemannstrasse.

A few narrow streets cut between the hulking modern architecture, which includes two high-rise office towers owned by Daimler, one of which was designed by star architect Renzo Piano. The round atrium of the Sony Center comes closest to rendering a traditional square used as a public meeting point. Farther down Potsdamer Strasse are the state museums and cultural institutes of the Kulturforum.

Kreuzberg held the American side of the border-crossing Checkpoint Charlie, and is one of the liveliest districts in Berlin. A largely Turkish population shares the residential streets with a variegated assortment of political radicals and bohemians of all nationalities. There are few traditional attractions here, but it's a great place to people-watch.