Wedged in between shops and garages on busy An der Malzmühle street hides a very special leftover of the Roman empire: the Ubiermonument (or Ubii Monument). Behind the facade of a nondescript office building from the 1990s hides a former tower of the harbour entrance of Colonia Claudia Ara Agrippinensium, the Roman colony in the Rhineland. When it was erected in the 4th or 5th century, this was a massive, 12-meter tall tower made of tufa blocks, which was subsequently incorporated in the medieval structure of Cologne. It was rediscovered in 1965 during building works and is today part of the exhibitions of the Roman-Germanic museum.

I always like to visit: that the Ubii monument is only open once a month lends it some added mystery, and entering from the busy street into the dim quietness of the exhibition space really makes it feel like peeling back the layers of Cologne history.