Rickety Old Bridge

First question: who built this nonsense? Second question: again?

The bridge that's lost some of its planks, is placed over a very dangerous pit of something (Bonus Points if it's something other than lava, water, or nothingness), and doesn't at all guarantee safety when crossing despite the main characters always being able to cross it, therefore negating any real feeling of suspense. The Rickety Old Bridge must be crossed so then our heroes can get across and progress the plot. There's almost always some doubt about crossing the Bridge since if someone was to fall off, they'd face the terror that's below them and die.