The oldest and most precious section of Aachen Dom is Charlemagne's Pfalzkapelle (palace chapel), an exquisite example of Carolingian architecture.
Completed in 800, the year of the emperor's coronation, it's an octagonal dome encircled by a 16-sided, two-story ambulatory supported by antique pillars from Italy.

Nikon D300, Nikkor 16-35mm F/4 IF ED VRii, monopod