We paid to cross the Kazura vine bridge. It doesn't look that scary (it was safe enough though, for you motherly types it's reinforced with steel cables, though they're well hidden) but it was! the spaces were just large enough and just wide enough to make the rushing water below look a little too close! This area, Iya Valley was a great place to hide and run from enemies in Old Japan. The vine bridges (there are several others) were used because they could easily be cut if you were being pursued!