This weekend, the Boston Public Library hosted a Lego building contest. I was a bit disappointed: I expected large diorama type things, and instead, they were small pieces. Nonetheless, there were some interesting entries. A caboose is loose:
Couldn’t figure out this one:
Guess this one:
The moose is loose!:
I think your second one is a Quidditch field at the start of play.
The one you couldn’t figure out is quidditch (Harry Potter reference) and the glasses are really goggles with a snorkel.
For large dioramas you want BrickFair, which is held in New Hampshire and is the closest large LEGO exhibition to Boston. The NELUG (http://www.nelug.org/) probably also participates in exhibitions in Boston sometimes, although it’s hard to tell since they rarely update their website.