If you enjoy just walking in the town and appreciate nice old buildings, doors, gardens ... Saarbrücken can offer you a great experience. 

Starting from the Sankt  Johannes Markt, which is located in the center of the town, walk in the small streets direction Mainzer strasse and around it, Bismarckstrasse and all the neighborhood around it, Grossherzog-Friedrich-Strasse and of course in the Nauwieser Viertel which is behind the Johannes Kirche. 

 Look at the fassades of the buildings, check the windows decorations, the doors, the roofs...  

See links below: 

Saarbrucken Architecture in Wikimedia

Saarbrucken houses album