Rheel was a planet located in or near Federation space within the galaxy's Alpha or Beta Quadrants. It was the homeworld of an extinct civilization.
History and specifics[]
Rheel had more than one ocean, continents, volcanic activity, and several islands.
In the 2260s, the Federation starship USS Enterprise orbited Rheel, discovering evidence of roads and buildings. Sensor sweeps pinpointed formations on a small island that seemed to be part of the planet's natural geology, but further examination revealed them to be a circuitous roadway. (TOS - Star Trek Annual 1986 comic: "A Hint of Life")