Lublin, Poland

Lublin sits in eastern Poland with roughly 340,000 residents, and its 1569 Union between Poland and Lithuania created Europe's largest state at the time. The 1317 Lublin Castle preserves a 14th-century Holy Trinity Chapel decorated with Russo-Byzantine frescoes, an unusual sight in Latin Europe. Outside its walls, the Krakowskie Przedmieście ranks as the oldest preserved civic avenue. Four kilometers southeast, the Majdanek concentration camp became a state museum in November 1944 — the first established on former camp soil.