The cave of time
You cautiously approach the spaceship and, to your amazement, see that it is resting a foot or so above the ground, without any visible mechanism keeping it aloft. There are no engines, rocket exhausts, port holes, landing gear, antennae, or any equipment you might imagine a spaceship would need. You realize it must be the product of a supremely advanced civilization.
Trusting that such people have learned to be loving toward others, you approach the ship. A portal slides open, but all you can see within is shimmering blue light. A large cube is thrust out through the portal and lowered to the ground by mechanical arms. The top of the cube is withdrawn, leaving a pallet on which lie the sleeping forms of three men and three women, dressed in shrouds of animal skin. Their bodies and features remind you of pictures you have seen depicting the earliest men on earth. You have an impulse to jump aboard the spaceship before the portal closes.