E

“Begin morning run,” I said to Max. “Bifrost track.” The virtual gym vanished. Now I was standing on a semitransparent running track, a curved looping ribbon suspended in a starry nebula. Giant ringed planets and multicolored moons were suspended in space all around me. The running track stretched out ahead of me, rising, falling, and occasionally spiraling into a helix. An invisible barrier prevented me from accidentally running off the edge of the track and plummeting into the starry abyss. The Bifrost track was another stand-alone simulation, one of several hundred track designs stored on my console's hard drive.”
― Ernest Cline, Ready Player One