"This is a message. Of the students. At the...American Embassy in Tehran."

Um, based on what I saw, I don't think this is entirely accurate. For one thing, there's no food, no beds, and no toilet in the box, so clearly they're not intending to spend the ENTIRE three weeks locked inside it. Presumably they'll "keep hours", and then sneak out after closing time when nobody's looking.

What they do have in there is a lot of raw material: lumber, bags of cement, what appear to be a number of metal framed panels, a workbench, and a bunch of tools, including a couple of bad-ass contractor's nail guns. So, my guess is, the end result will either be some sort of large, segmented installation piece, possibly maze-like in overall design, or else their planning one Hell of a round of "nail gun tag".