Chappel Rose Window

This window in a Chappel of the Cathedral featured here last week gives a new take on looking at life through rose glasses.

Alcessa already knows the location, but for the rest of you guys, here are the final hints:
– Oldest German town, just some 40 km east of the City of Luxembourg;
– Birthplace of Karl Marx;
– Only church in the area with a Coptic chappel (as of this year).