The Bridge in Moria from The Lord of the Rings: The Fellowship of the Ring. This bridge is constructed entirely from pink insulation foam and plaster. It doesn't really lead to or from anywhere, but it was fun to make.
The rocky walls are insulation foam covered in plaster of paris, detailed to make it seem rock-like. The paint is black followed by some dark reds and browns.
The bridge is just foam, with some plaster over the top to smooth it out a little bit. The painting is various shades of sandy brown over a black base with a hint of blue-green for lichens or possibly oxidized metals (the non-red oxidizing ones).
The pillars started as simple square columns, which i carved away at and also built up on with thin layers of foam for the base. They received the same paint job as the bridge.
Gandalf of course is a must for any such bridge.
Materials and related: