Starry Sky is an Expert Difficulty track. This track is unique because it has water (pond), Aerogel (clouds), and space (sky). You can place land towers on the moon, grass, and clouds. You can put water towers on the clouds and pond. You can place space towers on the stars and space. The only point of placing towers in the water is if you have a 4/x Buccaneer or a Pontoon with a big ranged tower. It is unlocked at Rank 25.