The cave of time
Much as you would like to see the inside of the alien ship, you have no desire to be whisked off into space. You step back to what you hope is a safe distance and watch what happens. In a moment the portal closes, and almost instantly the ship rises, silently, straight up. Within a few minutes it is lost from view. You walk over to look more closely at the primitive looking people sleeping on the pallet. They begin to stir and stretch and rub their eyes as if waking from a long sleep.