For a sense of why the ambiguity arises, consider how we experience geography in everyday life. We might suppose there is a unique “real” shape to the landscape—what Google Earth shows—but in practice the shape is defined by the experience of being embedded within that landscape, and that experience can vary. [...] When we eschew the view from on high, we can no longer make definitive statements about what is where.
In an epiphany in 1915, Einstein realized that the ambiguity is not a bug but a feature. He noted that we never observe places to have absolute locations, anyway. Instead we assign positions based on how objects are arranged relative to one another, and—crucially—those relative locations are objective. [...] If the landscape buckled or flowed while preserving these relations, the denizens would never know. So it is for spacetime.
[...] When we say it's located at such and such a place, we're really using a shorthand for its relations to other landmarks. Lacking definitive coordinates, the cafeteria must be situated by the things within and around it. [...]
General relativity confounds our intuitive picture of space as a kind of container in which material objects reside and forces us to search for an entirely new conception of place.