How to Build a Bridge
I just thought I would add a diagram for a basic bridge. I’m not an architect or anything so I’m sure this design can be improved upon. It’s basically just a frame made of 4×4’s or 2×4’s depending on how much weight it will need to hold, that rests on some 8-12 inch posts that are cemented into the ground. You can use trees for the posts or old telephone poles, whatever works.
For the hand rail I would just use some 2×4’s or you can even use some small trees that have been cut down to give it a rustic woods sort of look. The floor of the bridge would be 1″ plywood, or if you want you could lay 1″x6″ planks down. If you really wanted to you could make your own planks from downed trees or whatever(I wouldn’t suggest this).