What do you do with 1200 square feet of agricultural plastic foil, 400 feet of gaffer and masking tape, a piece of black cardboard and a nicely located office in downtown Budapest, Hungary on a sunny weekend? A giant camera obscura, that's what you do.
Once your eyes get used to the dark it's pretty cool to just lay down and watch the moving image on the wall, but we made a timelapse too (mirrored both horizontally and vertically to match what you'd see from the window):
And a longer version, with the setup/teardown included:
Image source and optical background: Wikipedia.