After Link crosses the River of Sand, he sees a series of flag posts that guide him to a monument in the middle of the Wasteland. From this point in the desert, if Link wanders off, he gets caught up in the sandstorm and automatically appears back at this monument near the River of Sand. At the top of this monument, there is a stone plaque that states that the eye of truth shall be guided to the Spirit Temple by an inviting ghost.
After using the Lens of Truth, Link is able to see the Phantom Guide. Link can then follow the Phantom Guide who zig-zags its way through the Haunted Wasteland, but in the process, Link encounters Leevers that try to distract him from following the Poe. As long as Link follows the Phantom Guide in the proper direction, he will make it to the Desert Colossus, where he finds the Spirit Temple.