From Kaiserslautern, it is a 5 hour drive, realistically. Online maps will say 4, but that is most likely not going to happen. The hotel tax in Konstanz gives each tourist a free bus pass, which we used to travel from old town to the island of Mainau (15 minutes). I was pleasantly surprised that we walked around Mainau for 4 hours, and could have stayed longer. The flowers and trees are beautiful, and the butterfly greenhouse was fun. Of course there are snacks to be had everywhere, from a nice café in the palm tree greenhouse next to the palace, to a modern restaurant near the harbor.
We departed Mainau from the harbor, taking a boat across the lake to Meersburg, then back to Konstanz. We’d like to return and take day trips by boat to towns around the lake. Most shops in Germany are closed on Sunday, but we lucked out with a special shopping Sunday in Konstanz. We snagged some superb Swiss chocolate, and perused unique clothing and book stores. There were also temporary tents with hand crafted items around the harbor area in Konstanz.The food was very good, if pricey. We ended up at only one vegetarian restaurant, Sol, which was terrific, but were pleased with the vegetarian choices at regular places (including Mainau). The border to Switzerland is at the end of the harbor area of Konstanz. You can walk through to the other side and save the 50 Euro sticker for your car. We didn’t spend much time on the Swiss side this trip, but would like to return and stay much longer all around the lake.