Ruby

Ruby is a dwarf moon in Io's East Orbit and the home of Ryld. Its small surface area is covered in an ecumenopolis of wooden skyscrapers. Devoid of life and lacking any native species of its own, Ruby was originally founded as a prison colony. It now thrives through tourism and culture. It is most famous for its Carnival, a Homyn holiday celebrating the moon's jubilee, rife wtih debauchery, masquerades and parades.
Ruby is one of the gem colonies--along with Topaz and Diamond--that were the second set of moons annexed by the Homyn Kingdom.