The water under Aachen smells of rotten eggs, and for two thousand years that has been the city's secret. Romans found it, Charlemagne built his capital on it, and thirty one German kings were crowned beside it. This self guided audio walking tour, narrated through the Tourific app on your phone, traces those springs to the cathedral, the apothecary that produced one of Germany's first chocolate bars, and the spot where Paul Julius Reuter trained pigeons to beat the telegraph. You will meet the Bahkauv, a sulphurous calf locals say climbs onto the shoulders of drunken men, and hear how a young baker once tricked the devil with a tray of hot Printen. Walk at your own pace, pause for a rice tart in a baroque café, and resume when you are ready. The audio runs offline.