Galileo Regio is a large, dark surface feature on Jupiter's moon Ganymede

Ganymede (moon)

Ganymede is a satellite of Jupiter and the largest moon in the Solar System. It is the seventh moon and third Galilean satellite outward from Jupiter. Completing an orbit in roughly seven days, Ganymede participates in a 1:2:4 orbital resonance with the moons Europa and Io, respectively...

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Contrary to the first impression, Galileo Regio is not an impact crater but a region of ancient dark material that has been broken apart by tectonism and is now surrounded by younger, brighter material that has been upwelling from Ganymede's interior. It is thought to be some 4 billion years old and is heavily cratered.

The regio is bounded on the south by the Uruk Sulcus

Uruk Sulcus

Uruk Sulcus is a bright region of grooved terrain adjacent to Galileo Regio on Jupiter's moon Ganymede. It is thought to be younger than the darker material elsewhere on the moon....

 region, which lies betwixt it and Marius Regio.
Within Galileo Regio itself lies Memphis Facula

Memphis Facula

Memphis Facula is a palimpsest, or "ghost crater", on Ganymede, the largest of the Jovian satellites.Some 340 km across, it is situated in the south western part of Galileo Regio, a huge almost circular dark region on Ganymede's north eastern flank...

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