Excerpt taken from TheFoxIsBlack:

When I first saw Junya Ishigami’s Cuboid Balloon all I could think to myself is how it looked so immensely heavy yet it was like it was floating at very same time. How can something look like and heavy at the same time? It’s nonsensical, but when you look at the Cuboid Balloon it’s hard not to ponder this duality. It was constructed in the Museum of Contemporary Art in Tokyo and is actually an aluminum truss (which weighs over a ton) that’s filled with helium, so it’s actually floating. Don’t believe me? Well thankfully I found a video of the installation where you get to see a person, I’m guessing museum staff, grab a corner of the balloon and bring it closer to the floor. Pretty amazing stuff.