Ganymede which is a moon in our solar system has an underground ocean that contains more water than all the oceans on Earth

 This would mean that oxygen to breathe and hydrogen to burn or to do hydrogen fusion rocketry with are all there on Ganymede. Ganymede is one of the moons of Jupiter. So, if someone with enough technological knowhow got there they would have water and oxygen and hydrogen from the water to travel further than Jupiter eventually.

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Ganymede's underground ocean contains more water than all the oceans on Earth. The solar system's largest moon, Ganymede, in orbit around Jupiter, harbors an underground ocean containing more water than all the oceans on Earth.

Huge ocean confirmed underneath solar system's largest moon