The southern of the two "fingers" of Lake Constance is Untersee (Lower Lake). Many tourists miss this part, which is a pity, because Untersee is a dream! Sometimes it is rather river-like, then again wide and open. Nowhere is Lake Constance more varied. You shouldn't miss the Rhine Falls and the Höri peninsula!
The slightly hilly route repeatedly offers wonderful views of the water and the island of Reichenau, the Höri peninsula and the Schiener Berg. Lake Constance ends in Stein am Rhein and the (High) Rhine begins again. The small medieval town with its painted houses, the town hall square and the Werd monastery island off the shore is rightly a tourist magnet.
If you are already in Stein am Rhein, you should definitely make a detour to Schaffhausen and the Rhine Falls. A boat trip to the Rhine Falls is absolutely stunning, especially in May and June when the river is at its peak after the snow has melted. If you want to cycle the whole route there and back, prepare yourself for almost 50 hilly kilometers!
The climbs in Kattenhorn (short but steep) and between Wangen and Hemmenhofen (longer but moderate) should not deter anyone from cycling along the Höri peninsula. This section of the Lake Constance cycle path is fantastic!
This section of the Lake Constance cycle path is practically free of climbs, but not particularly interesting either. So you won't miss much if you shorten the route here by train.