A long vine is an item used to cross a river in Temple Trekking. To make this, players must use use the "trim" option on a swamp tree next to the river to obtain three short vines. The three vine sections are combined by using them on each other, forming a long vine which is then lassoed over a swamp tree to form a rope swing to cross the river. The long vine is lost in process, and therefore cannot be taken outside of the minigame.
Note that it is necessary to click the "Lasso" option on an upper branch of a swamp tree, rather than using the vine on the tree.