A megadisk is a galactic megastructure shaped similarly to an Alderson disk but significantly larger, constructable with significant effort by a Type 4.0 civilization and routinely by Type 5.0 civilizations and above. They have a radius of 10 light years and a central hole with a radius of one light year. Inside the central hole is a quasar, which provides heat and light to the megadisk. It is habitable on both sides; the mass of the structure of the megadisk provides gravity, as well as artificial gravity.