Paleoloithic images which appear curiously non-human

[Mystic Wanderer]

I don't think the ETs feet extend below the "ladder", as he called it. I think they are sitting at the controls. It appears he drew the feet in. Look at the original and you will notice this.
The wavy lines represent the propulsion that makes it fly, and the "ladder" is not a ladder, but a band device that goes around the ship to control the anti-gravity.