Unsmooth grassy surface
Wood chips
Undefined surface
Slippery trail
Aqueduct - A ditch or a chute to divert water
Bridge - A structure that carries a path/trail/road across a waterfall, river, ravine or other obstacle
Step - A step, ledge, stair or low ledge that must be stepped on
A ford - Unbridged river/a stream, wetland or a swamp
<1m - Less than one meter