As a possibility for lunch, the Zeughauskeller is a hoot, just of the main street between the station and the lake, Bahnhofstrasse, and served good Swiss-German style food. I had an enormous schweinehaxen there, and it's decorated with various styles of armaments. I was going to suggest a circle trip on the passenger ferries on the lake, but that might take up too much time. I can't recall, but I think it was more than 90 min. It is a nice ride, though, if the weather is nice, and starts early (~8). Station/dock where Bahnhofstrasse hits the lake.