Cologne Cathedral took 632 years to build. Construction began in 1248, stopped entirely in the 1500s when Gothic fell out of fashion and Protestant pilgrims stopped bringing money, then resumed in 1842 and finished in 1880.

The choir, completed in 1322, is the most medieval section. Workers built it without construction drawings, hydraulic machines, mathematics or computers, relying only on sketches in sand or parchment and what existed in the master builder's mind.

Legend claims the first master builder, Gerhard, bet the devil he could build the cathedral faster than the devil could build 100 kilometres of water pipe to Cologne. The devil won. Gerhard jumped from the scaffolding in despair, and the devil transformed into a dog, caught him mid-air, and dragged him to hell. Many believed this cursed the cathedral to remain unfinished.

The golden shrine inside holds relics of the Three Magi, which drew thousands of pilgrims from across Christendom in medieval times. With 50,000 inhabitants, medieval Cologne was larger than Paris or London.

VoiceMap's self-guided audio tours explore how the cathedral shaped medieval Cologne's prosperity, trace the devil's curse through 600 years of interrupted construction, and reveal why craftsmen today have work scheduled until 2070.