I have collected some of my beer caps since moving to Aachen, as my idea is to one day incorporate them into the bar I want to build in my basement someday. The highlight here is focused on the Trappist Westvletern 12 cap, which is often rated as the best beer in the world, partly because it is only sold first person by the monks at the monistary. Although a black market exists, and I received a bottle of 12 for my 30th birthday from my lovely wife and my brother in law Dave, and I recently enjoyed it and it did not disappoint.
