Well, a bridge, anyway.
I was busy breaking out my terrain boards for this afternoon, when it occurred to me that a river without means of crossing it wasn't much cop as a terrain feature.
Time to get busy - five coffee stirrers (some of the last of my swag from the BBC and East Coast trains!), a handful of matchsticks, some superglue...
I omitted to grab some photos of the construction, but basically it's two H-frames of matchsticks, with a split coffee stirrer 'plank' as a cross brace.
The decking is four coffee stirrers, joined at the ends and middle with a smaller cross-piece, and a matchstick as well. Final step is to sit the decking on the H-frames, hold it till the glue dries and then add two more cross braces from split stirrers.
Liberally stain with Army Painter dark tone ink (I may add another coat), and bob's yer uncle: one small ramshackle footbridge in 28mm or larger bridge in 15mm.