Aliens???

I spotted these yesterday as I drove by our friends' house... I didn't slow down to take a closer look, until today.

All in a row.
Thought I'd better investigate.
Wanted to see if there were "wee folks" climbing down outta there.

Could this be the result of toppermost-atmospheric-incomprehensible-heat and burn-upon-entry?

And... might this be the Command Center?

Are you with me? I'm going Down Under!
Taking a peek... AAAHHHHH!

Hey... it's Beautiful down here!I don't see a sign of anyone,
but this thing is HUGE!
I feel like a little, bitty fellow...
Wonder if I could crawl up this "tree."
If I could just get up to that ring.

(If you don't hear from me pretty soon,
please call home.)

It's Shady under here, too!