Out of all the great-value apartments, luxury mansions and weird and wonderful holiday homes, which Airbnb is the most popular of them all? Well, according to Airbnb it's a tree house, a small, intimate property hidden in the trees, literally, in Aptos, California. The Mushroom Dome Cabin has just one bedroom. It's been listed for nearly 10 years, and is the most-booked property ever on Airbnb. If you want to enjoy a one-night stay, you'll need to book five months in advance!