Under Cologne's town hall there is a Roman palace, and you can walk through it. The Praetorium was the residence of the governor of the province of Lower Germany, a large building complex on the edge of the Rhine that dates from the first century and grew over the next few hundred years. The city, called Colonia Claudia Ara Agrippinensium, was founded in the first century AD and named for Agrippina, the mother of the emperor Nero, who was born in a camp nearby. The remains of the palace were found during rebuilding after the Second World War, and the cellars and corridors are now open as an archaeological site.
The Praetorium belongs to the Lower Germanic Limes, the Roman frontier that followed the Rhine to the sea, which UNESCO added to its list in 2021. Cologne was the capital and the largest city on that frontier. Close by you can find the Roman-Germanic Museum, beside the cathedral, where the Dionysus mosaic is on display in the room where it was found, and the Roman sewer and the stretch of Roman wall, which show how substantial the city was.
For a rider, Cologne is an urban visit and needs a different mindset. The old town is mostly pedestrian, with cobbles, trams and many one-way streets. Cars and bikes are numerous, and the city has a low-emission zone, so check whether your vehicle meets the rules before arriving. The ride in along the Rhine from Bonn or Düsseldorf is flat and broad, and the cathedral appears on the skyline long before you reach it. The twin spires of the Dom, a huge Gothic building begun in the thirteenth century and finished in the nineteenth, are best seen from the other side of the river, near the Deutz bridge.
With almost a million people, the city has fuel stations, supermarkets and bike parking in plenty, though a quiet side street is easier to find than a space in front of the cathedral. Weekdays are heavy with commuters, and Sunday mornings are calmer. The local drink is Kölsch, a pale, light beer served in tall thin glasses by waiters in blue aprons, and the local pub food, Halve Hahn, is a rye roll with cheese, which has nothing to do with chicken. Allow an hour for the Praetorium, and an evening for a stroll beside the Rhine.