K'Nex master Austron is constrcting the world's largest K'Nex ball machine. It's located at Bloomington, Minnesota's The Works museum. Austron says:

The machine stands 23.5 feet tall and 40 feet long, and contains over 100,000 pieces. It has 2 lifts, 3 motors, and 8 paths, including a 20 foot free-fall, an 8 foot tall big-ball-factory spiral, and a 60 foot long path which hangs from the ceiling. It takes 3 and a half minutes for a ball to climb to the top of the tallest tower.
"World's Largest K'nex Ball Machine - Teaser" (via Smithsonian)