mar zald
Google
When in Regensburg, you must go see the Porta Praetoria. It is a gate preserved from Roman times. From what I understand, this was the Northernmost gate to the Danube River.  It is only partially preserved  but it is still such a cool sight to see when you are walking down the street and you see it. For me, it's always as great to see it as it was the very first time that I came across it, purely by chance. There is so much Roman history here.
This city is so cool.
It is located right behind the Regensburg Cathedral ( The Regensburg Dom). So, you make sure that you are on Domplatz then keep on walking, following the curve of Domplatz, it will curve to the right. Follow it, and the street becomes Krautermarktstraße. When you reach the end, turn right and you will be on Goliathstraße. Stay on it and it becomes Unter den Schwibbögen. You will immediately see the big Porta Praetoria  to your right.