Wheeeee!

These huge lumbering creatures aren't hostile, and can be found all over the place just chilling around.

You can either build up to their level and attempt to jump over to one - or, once you've unlocked the Jetpack (early/mid game) you can use that; one charge is enough you get you from ground level up to bounce on their back.

Bounce.. ....yes, if the creatures weren't weird enough already, they are indeed bouncy!