The Celestial Toyroom is a dimension created by the BBC in 1966 for Doctor Who.
The Celestial Toyroom is the realm of the Great Old One, the Celestial Toymaker, a remnant of its original universe and an integral part of the entity. The Celestial Toymaker could not survive long outside of this reality, due to the rules which were set down in his own home universe. He resides in the "Toy Shop" which unlike the rest of the realm is actually connected to him. Everything else can be destroyed except for the Toy Shop. A void surrounds the Toy Shop and anyone who attempts to leave, find themselves in a loop reentering it.
Interestingly, several of the entities appearing within the Celestial Toyroom seem to be fictional creations with their own independent "life", similar to Dreamlands entities.