Saturn would float on water

If a bathtub big enough existed, Saturn would float in it.

Despite being a giant —more than 700 Earths would fit inside— it's made almost entirely of gas, mostly hydrogen and helium. Its average density is lower than that of water, so, in theory, it wouldn't sink.

It's the only planet in the Solar System you can say that about. All the rest, Earth included, would go straight to the bottom.