The Flying Nimbus is a small cloud that will fly the rider any where, but you must be pure of heart to ride on the Flying Nimbus, otherwise you will fall straight through it. Master Roshi gifted the cloud to Goku after he helped Turtle find his way back to the ocean. Master Roshi was no longer able to ride on the cloud anyways. Bulma and Oolong have also been shown not to be able to ride on the cloud, but Chichi was.