The Plank Bridge is a floor you can build (the Outdoors page).
In-game description
Planks on posts, laid over water: a bridge across a river, or a dock out into a lake. Walk on it dry.SHOWN IN THE BUILD RING
Building it
It costs 3 
Wood, 1 Earth 1 Water spirits. Take it down with DISMANTLE to get its cost back (see Building).
