A pleasant world in the Omicron Delta region whose hidden machinery creates whatever visitors imagine, visited in Shore Leave and The Animated Series.
The Shore Leave planet is a lush, Earth-like world in the Omicron Delta region that appears ideal for crew recreation. In Shore Leave, landing party members begin seeing things from their own minds, including the White Rabbit and Alice, a samurai, Kirk's old tormentor Finnegan and his former love Ruth. Some of the encounters turn dangerous, and McCoy appears to be killed by a knight.
The planet turns out to be an amusement park built by an advanced race, with machinery beneath the surface that reads thoughts and manufactures them. Its Caretaker explains that no one is truly harmed, McCoy is restored, and the crew is invited to enjoy their leave.
The Enterprise returns in the animated episode Once Upon a Planet, where the planet's master computer, resentful of serving after its makers are gone, turns hostile.