Kreuzberg, a part of the combined Friedrichshain-Kreuzberg borough located south of Mitte since 2001, is one of the best-known areas of Berlin. Kreuzberg, colloquially also known as X-Berg, is often described as consisting of two distinctive parts: the SO 36, home to many immigrants; and SW 61, roughly coterminous with the old postal codes for the two areas in West Berlin.