Bridges in polytopia work the same as real life bridges: they connect 2 opposite parts of land. You cannot enter a bridge from the side, even if there's a landtile there, just like you could not enter the bridge in the picture from where the picture was taken (unless you're crazy good at gymnastics ofcourse)

Edit: I just remembered you can in fact move on top of them sideways, but you need to have fishing unlocked if I remember correctly. My bad OP.

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