The eight previous worlds have left the Earth awash in the transdimensional. Devices, prior-world structures, and even many of the creatures featured in the Numenera corebook, like the abykos and the Nibovian wife, are entities that exist partially out of phase or hail entirely from another plane. At least one of the prior worlds explored and harnessed alternate dimensions as a means for increasing their own power and knowledge. Many of these entrances and exits still remain.