A zip line includes a substantially rigid track supported above a ground surface by a plurality of supports, a trolley which moves along the track, and a rider support suspended from the trolley. The track is comprised of a plurality of track segments connected together such that adjacent track segments have substantially no freedom of movement relative to each other, and such that adjacent track segments present a substantially smooth, continuous, and uninterrupted surface. The track includes a run and a flange extending upwardly from the run. The trolley comprises a frame having upper wheel mounts to which first and second upper wheels are rotatably mounted. The first upper wheels are oriented such that they engage an upper surface of the track run and the second upper wheels are oriented such that they will engage the track flange upon rotational movement of the trolley relative the track run.