The Elf-path was a means of crossing the forest of Mirkwood.
Beginning at the western edge of the forest north of the Carrock, the Elf-path ran from the Forest Gate into Mirkwood, and led straight through the forest to its end, near the Forest River.
The Enchanted River crossed the Elf-path nearly three quarters of the way through.
History
The Elf-path was wrought by the Elves in the Third Age of the Woodland Realm probably when Sauron occupied Dol Guldur and the forest became filled with evil things. Being the safest route through northern Mirkwood, Gandalf chose this way for Bilbo and Dwarves to take to the other side during their quest to the Lonely Mountain. It may have survived into the Fourth Age.
In adaptations
In The Hobbit: The Desolation of Smaug before departing, the wizard Gandalf warns Thorin and Company to take the Elf-path, as it was the safest route through Mirkwood to the Lonely Mountain. However, Nori accidentally leads the company off the path, causing them to look for the path again.