>> an visualise every step and turn of a journey of hundreds of miles, while being shoved through space at roughly 20 times normal walking speed, and do this for many different journeys.

That is nothing. Try to run through a forest chasing a deer. Your brain will be calculating paths around trees, planning each footfall based on 3d terrain scans in your peripheral vision, constantly recalculating the position and likely path of the deer, and all the while a subroutine is calculating the trajectory of the rock you are about to through at your (hopefully) future dinner. That is what the human brain evolved to do. In comparison, driving a car along a road is like watching paint dry.

Then think about what the deer brain is doing. It does all the same terrain mapping and 3d planning, but does so at double or triple the bandwidth. Deer see 300+ degrees, humans only 130ish.