Perception of Time and Space.

[Fang]

It's an illusion in the sense that you are misinterpreting your experience.

We can't travel through space without traveling through time and vice versa.

That's because you don't travel through one or the other, you are always moving through both (space/time, and really both are the same thing). "Clock time" as a (functional) social institution is as zm said above, not actual "time" and the effect of using clock time in society has led to most people unconsciously divorcing "time" from space.