The Space Warping Spell was a very unusual spell taught to Eragon by Umaroth and the other Eldunarí from the Vault of Souls. The exact nature of the spell is not known with certainty but it seems as if it allows the person who casts it to create an invisible pocket of space to store objects in. After leaving the Vault of Souls, Umaroth has Eragon cast this spell on the Eldunarí, allowing them to easily travel with him to Urû'baen to confront Galbatorix.
According to Umaroth, this spell was discovered by a hermit who lived on the northern coast of Alagaësia 1200 years prior to the Rider War. Though it has not been empirically confirmed, it is strongly implied that this hermit may have been none other than Tenga, the former master of Angela the herbalist.