Best non animal related zoo exhibit

[ZooNut23]

In a similar vein to a thread I posted recently about lego in zoos...

What's everybody's favourite non-animal related zoo exhibit?

Mine is the tractor museum at Northumberland Zoo. It seems a fairly comprehensive collection. I'm not a tractor enthusiast by any means but I feel like it's raised my awareness tenfold

 

[Fallax]

I can think of a good number of impressive plant exhibits in zoos.

I feel like the slime mold exhibit at Vincennes is also worth a mention.