Okay, so you can't technically buy anything at the Aalsmeer Flower Auction — unless you're running a flower wholesaling business — but that doesn't mean it's not worth the trip. Open to the public on Mondays, Tuesdays, Wednesdays, and Fridays, the world's largest flower auction is a sight to behold, with self-guided and guided tours available. Roughly 20 million flowers are sold at the auction each day, and the building itself is the world's fourth-largest by floor space, covering 10.6 million square feet, or 243 acres. So way more than your garden at home.