Saddle Rash (2002)

S1E19 Gilligan Meets Jungle Boy

Gilligan stumbles upon a boy raised in the jungle while on the island. The boy reveals a mysterious hole in the ground that makes things float. The professor hypothesizes that it could be releasing helium or hydrogen. Excited by the discovery, he quickly begins constructing a massive balloon, aiming to use it to transport one of them back to society.