Colmar-Berg is a commune and town in central Luxembourg, in the canton of Mersch. It is situated at the confluence of the rivers Attert and Alzeā¦Colmar-Berg is a commune and town in central Luxembourg, in the canton of Mersch. It is situated at the confluence of the rivers Attert and Alzette. Colmar-Berg is the site of the Grand Duke of Luxembourg's principal residence, Berg Castle. It is also the site of a Goodyear tyre factory.