Cent is an enormous mage city at the center of the Earth (thus its name). It was created approximately 500 years ago when a powerful channeler, Millicent Goodwyn, the last Finder, made "The Journey" as it is known by the Lit. She famously created an energy sphere (similar to the energy sphere originally created to protect Atlantis) that she guided from an entrance near volcanic activity in the Pacific ocean to the center of the Earth over a 40 day period.
Atlantis is the largest and most ancient of the underwater city states. It is surrounded by a similar energy sphere to Cent's, and many of the most ancient races, including the Rauks, rule the city state. It is on the ocean floor in the Pacific Ocean, and is a wondrous in its splendor and ancient architectures. A second, much larger energy sphere surrounds the core air-filled energy sphere, bringing light and less pressure, allowing many different water species to exist at depths they normally would not be able to live.
Tierra Dura is one of the most important of the underground mage city states. It is not the largest, but it is one of the most magically and technologically advanced cities, and is known world-wide as an innovation hub. It is a large city under the Sandia Mountains near Albuquerque, New Mexico. Entrances are hidden by magic, but once inside Tierra Dura, a magical field allows a view of the sky as if the top of the mountains were not there.
There are many small, but growing, Lit cities on the moon and other planets. All of the Lit space cities are enclosed by energy spheres like those of Cent and Atlantis. The largest city on the moon, home of the Mentis society, is itself called Mentis. There are two larger cities on Mars, one larger city on Venus, a city in the atmosphere of Mercury, and cities on several of Jupiter's moons. Mages built flying ships in the early 1800's, which were able to travel through space. Initial colonies were established, and quickly grew and expanded over time.