Friday Pop Quiz (because summer will eventually get here)!

I keep this photo on my desk bulletin board. I found it in some files years ago (i.e. credit is not mine).

This is probably an easy one, but a fun one. Quiz: What is this structure? 

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And tell me, what are you up to this weekend? Anything fun? Good weather? The snow is practically all melted in Burlington (hallelujah), at least until we get a good April storm. 😉