Do not believe a single thing the people on that show say. They're lying.
While it's possible that some of them mean well and are just misguided, the overwhelming majority of them are deliberately misrepresenting the truth in order to sell you stuff. The genuine scientists on the show probably aren't lying, but frankly, I question the judgement of anyone who appears on that show and isn't a kook trying to sell you a magic healing stone.
Let's just take a few examples from that particular episode. Firstly, Göbekli Tepe, the prehistoric megalithic site in Turkey. It's a pretty impressive, even revolutionary archeological find, but that doesn't stop Alien Hair Guy and his buddies lying about it. For crying out loud, the Wikipedia page I just linked tells us that even though the show says the opposite, both flint stone-working tools and the quarry the rocks were cut from have been found at the site. So there's no mystery whatsoever to how it was constructed. By people. With tools. No extraterrestrials necessary for assembly.
Much of the rest of the episode is set firmly in woo-land, with the usual wild narrative hopscotch ("if so...") and straight-up nonsense like the vimana dude walking among the Carnac stones and talking about their mystical auras. The bit set in the Americas does contain one of my favorite Ancient Aliens lines ever, when one of the "experts" explains that some of the Inca stonework has been exposed to large amounts of "thermal heat". The best kind, really.
By the way, they seem to mean vitrified stone. In both this and a previous episode, Ancient Aliens seems to treat vitrification as something that happens when an alien shoots a ray gun at a stone block. In reality, it just means the stones were exposed to fire. It may have been done deliberately, although it actually weakens the stone. Now, stone age people might not know that, but surely the aliens would. In my mind, their suggestion that the Inca built using alien rock-melting technology is completely ridiculous. If you have what basically amounts to concrete and want to build a wall, certainly you'd build a mould of the wall and pour in the concrete, as opposed to molding thousands of different-sized stone blocks and fashioning a wall out of them. But never mind that, here's an Inca shaman with a censer, and he says woo.
But it's the already mentioned Carnac stones that bring us to the most fantastically stupid claim in the whole episode: Alien Hair Guy tells us they're one of only three objects on Earth that are visible from space. He lists the Carnac stones, the Nazca lines (a perennial Ancient Aliens favorite) and, of course, the Great Wall of China.
Now, once again, there's a Wikipedia page: Man-made structures visible from space. It will tell you, if you don't know already, that from any altitude where the Great Wall is visible, so are a whole bunch of other things. The same goes for the Nazca lines, and as for Carnac, well, look at them:
The individual stones are really quite small, and if they're that evanescent in an aerial photo, do you really think they're uniquely visible from space? The claim is totally absurd. Then again, that information and the picture are from Wikipedia, and if you're liable to believe Alien Hair Guy, you probably think Wikipedia is a reptilian disinformation operation. Like this blog. Boo!
In fact, I couldn't find any source for the notion that the Carnac stones are visible from space... except Alien Hair Guy. Mostly the claim appears in the exact same "one of only three objects" form he made it in. So he literally made that up. And that's really what this show is about: making stuff up. Specifically, inventing totally implausible claims with no regard for observable reality or even Wikipedia-level research. Since just about everything I've ever fact-checked from that show has turned out to be just lies, I frankly recommend no-one believe a thing that's said on it without double-checking it. Even better, don't watch the damn thing at all. Nothing they've ever presented has any merit, and the joke gets kinda old pretty quick. Real history is much more interesting, exciting and even, at times, mysterious than puerile "lol aliens" TV.
Ancient Aliens does take your mind to another dimension. Unfortunately, it's made up, and it sucks.