There is a magic Boundary (usually just called the Boundary) just two days travel into the forest that confuses travelers and sends them walking back the way they came – flawlessly. This has been there as far back as the Elves remember, and is to keep them protected as well as their forest protected, but it is also there to keep other races safe, as not every being can survive the dangerous beauty of the Forest of Tarathiel.
The Elves living in Elilona often make bets while watching travelers wander into the Tarathiel Forest to see how long it will take them to get confused by the Boundary and turn around. The stronger the will of the traveler the longer they last, but almost every traveler does not make it past the Boundary.
This is why when those same travelers tell their story in a tavern later they always tell of the unnatural sound of the Elves laughing, just out of sight. Sometimes they even tell of hearing otherworldly music playing from just the other side of a tree or the like, but can never quite find the Elves.
Nobody knows when it was formed, and its source is somewhat mysterious, but some believe that there is an ancient shrine in the Tarathiel Forest that powers the Boundary.