Ponttor is one of Aachen's surviving medieval city gates, a chunky defensive structure that once guarded the northern approach to the imperial city. Its tower, outer gate, and traces of the old fortification system make it one of the easiest places in Aachen to picture the walled city before modern streets spread around it.
It is a quick visit, but a good one. Walk here from the cathedral quarter and you get a useful contrast between Aachen's sacred imperial centre and the practical architecture that protected the town around it.