Several distinct WWII narratives
Holocaust history (Berlin, Krakow, Amsterdam), Western Front liberation (Caen, London, Bayeux), Eastern Front and partisan resistance (Warsaw, Belgrade), occupation experiences (Paris, Oslo, Copenhagen). Cities below specialize in each.
Berlin
Berlin Memorial to the Murdered Jews of Europe (2,711 concrete stelae, 2005), Topography of Terror (former Gestapo HQ site), Jewish Museum Berlin, German Resistance Memorial Center, Wannsee Conference House. Berlin is the most thorough city for confronting Nazi-era history. Mitte base.
Krakow
Krakow itself has Schindler's Factory Museum (Oskar Schindler's actual factory, now museum) and Kazimierz Jewish Quarter. But the city is mainly the gateway to Auschwitz-Birkenau (60km west, day-trip 6–8 hours). Free entry to Auschwitz; reservations required; guided tour mandatory peak season.
Caen and Bayeux
Caen Mémorial Museum is the comprehensive WWII museum. Bayeux is the closest base for D-Day beaches (Omaha, Utah, Sword, Juno, Gold) — all 30 minutes by car. American Cemetery at Colleville-sur-Mer above Omaha Beach.
London
London Churchill War Rooms (the actual underground bunker, preserved exactly), Imperial War Museum (multiple sites), HMS Belfast, RAF Museum (Hendon). Strong British Home Front and Battle of Britain narrative.
Warsaw
POLIN Museum of the History of Polish Jews, Warsaw Rising Museum (the 1944 uprising), Pawiak Prison Museum. Warsaw was destroyed and rebuilt — the entire city is essentially a WWII memorial.
Amsterdam
Amsterdam Anne Frank House (the actual annex). Reservations 1–2 months ahead. Verzetsmuseum (Dutch Resistance Museum). Hollandsche Schouwburg (deportation site).
Strategy
Auschwitz-Birkenau day-trip 8 hours emotionally heavy — don't combine with sightseeing. Berlin needs 2 days for full WWII coverage. Caen + D-Day beaches need rental car for full coverage. Free walking tours often WWII-themed.