One particular point that seems obvious after reading, but would not have occurred to me: If you ask a sighted person to imagine a nearby and distant object (say, a car), the distant object is imagined as smaller than the nearby one. But that distance / visual size relationship is a totally visual thing because you're imagining seeing the objects; a blind person's mental model of the object would be built from touch and is the same regardless of distance. They don't have the visual perspective cues. (If the object make sounds, I suppose it's imagined as quieter?)

To take that a bit further, I'd guess that blind people's metal models of geometry, whether it's a small object or navigating within a building, is purely orthographic in nature. They wouldn't have any use for our ideas of visual perspective, field of view, lines of sight, or any of that. Artists didn't work out how to replicate it properly until the renaissance, so it's not as though people have an innate conscious grasp of how it works; we just understand perspective as an innate part of our sight.

And on the other hand, the blind probably have a much more developed model of spatial acoustics: changes in reverberation as you pass an open doorway, move from a corridor into a larger space, etc., which our brains for the most part don't learn to build.

In any case, it's never a good idea to question someone with a different set of abilities than you have with a "is it really that hard?" Their experience far outweighs your naive intuition about what's easy and hard for them.

I guess you would have to describe them. As a suggestion - and not an attack in any way because I'm not sure how I'd do it! - without reference to anything you can see with your eyes, how would you describe space?