The Baedeker air raids by the Luftwaffe during WWII were so-called (by both sides) because they targeted cities such as Exeter Norwich, Bath and York – cities of historic or cultural ‘3-star’ significance, as highlighted in the popular Baedeker tourist guides. The raids were instigated as a reprisal for the bombing of the North German towns of Lübeck and Rostock by the RAF in March and April 1942.  The raid on Canterbury, on 1st June, followed the devastating Allied “1,000 bomber raid” on Cologne on the night of 30/31 May 1942.

Wikipedia