We have not yet fully explored the water laboratory. Still, I wonder how Doctor Tully or BURGL got there. After all, they must have been totally soaked.
1. So how about a submarine? This can be built from a nut. At the back a paddle wheel.
2. And how about paddle boats? With the floating flags, a separate track could be created, on which you can then race. Frogs announce the winner at the finish.
3. The last option would be a back motor. As with James Bond.