When the weather warms, there's no better way to explore Bodensee (Lake Constance) than with your bum in a saddle. The well-marked Bodensee Cycle Path is a 273km loop of Lake Constance, taking in vineyards, meadows, orchards, wetlands and historic towns. There are plenty of small beaches where you can stop for a refreshing dip in the lake. See the website for itineraries and maps.
Bike hire is available in most towns for between €10 and €20 per day. While the entire route takes roughly a week, ferries and trains make it possible to cover shorter chunks, such as Friedrichshafen–Konstanz–Meersburg, in a weekend.