The special exhibit was:
Many of the buildings were local Philadelphia institutions, but these are some of my other favorites are below. The entire exhibit is made out of natural materials, and appear to be bio-degradable. There's no information available about how the buidlings were constructed, which would have been really interesting, but they appear to be thin wood with a lot of epoxy of some kind. The trestles are made of wood.
Guess where you're NOT ?
Detail from Independence Hall: