A planet in another universe near the galaxy's center, where differing physical laws allow the Megans to practise magic.
Megas-Tu is the homeworld of the Megans, located in a region of space reached through an energy vortex near the center of the galaxy. Its physical laws differ from those of normal space, so that magic and witchcraft are real.
In The Magicks of Megas-Tu, the Enterprise is drawn there and the Megan Lucien shows the crew around. The crew learn to work magic themselves, but the other Megans, remembering their persecution on Earth, put humanity on trial before letting the ship leave.