Jewish Ghetto in Terezín is a must.
Take a direct train from Prague to Bohušovice nad Ohří station, then walk through this cozy little town to Terezín proper.
The whole town is actually a memorial to the sorrowful and shameful events of the WWII.
Address: EU, Czech republic, Bohušovice nad Ohří + Terezín
First published in the Levinarium Telegram Channel (now closed and deleted)