In the Guide, Magrathea is the planet of the planet-builders. Orbiting the twin suns of Soulimis and Mahr, the inhabitants of Magrathea use hyperspatial tunnels to create custom-designed planets for the richest of the rich. It is discovered that mice commissioned the creation of the Earth by the Magratheans, and did so again after the original was destroyed by the Vogons just before the program (which is what the Earth was) was complete. In the radio version of the Guide, the ruins of Magrathea were used to build the restaurant at the end of the universe, Milliways.