The city of Cologne, Germany has a long and interesting history.  When I visited the city, everywhere I looked there was some reminder of ancient and Medieval cultures.  Much of Cologne was destroyed during WWII, but an impressive amount remains.  And, nothing is quite so impressive in Cologne as the Kolner Dom/Cathedral.  Beyond being an excellent example of Gothic architecture, as well as an UNESCO World Heritage Site, it is a beautiful building.  Construction began in 1248 to house the reliquary of the Three Kings (a giant golden box supposedly containing the bones of the Biblical Magi) but the cathedral remained incomplete until the 19^th century.  Consequently, the Dom has a multilayered history from the ground-up.  The interior of the Dom is everything you could possibly want from a cathedral: beautiful stained glass windows, mosaics, murals, ornate altars, etc.  After exploring every inch of the nave, you can actually hike up one of the towers and lookout on the city (I can’t imagine doing that climb more than once).

Around and underneath the Dom are Roman ruins of various sizes, from a random wall or arch to larger architectural remains.  Just meander over to the parking garage near the Dom and you’ll find a lovely bit of Roman ruins.  Within the Cathedral Treasury, which houses an amazing assortment of ecclesiastical robes and jewels, you can also view the grave goods of two Frankish burials of a woman and a boy.  Ah, a structure to fulfill every need of a history/archaeology nerd.

To learn more:

http://whc.unesco.org/en/list/292