The Ponttor can be visited
City Wall Aachen-Ponttor

The Ponttor in Aachen is one of the last remaining city gates of the former Free Imperial City. As part of the outer city wall, it once served to protect the northern approaches and continues to shape Aachen's cityscape to this day.
History+
Construction of the Ponttor dates back to the early 14th century. At that time, new settlements and churches outside the original city walls necessitated a second, expanded fortification. The gate was one of eleven city gates surrounding the city, and along with the Marschiertor, it is one of two that have survived to this day. In the 17th and 18th centuries, it was occasionally referred to as Brückenpforte or -thor.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Ponttor_aachen.jpg
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 50.7816, 6.0782