There's what's in space, and what we don't know about

right here on the planet.

Archaeologists have harnessed sophisticated technology to reveal lost cities and thousands of ancient structures deep in the Guatemalan jungle, confirming that the Maya civilization was much larger than previously thought.

Experts used remote surveying technology to see through the thick canopy of forest, revealing more than 60,000 structures in a sprawling network of cities, farms, highways and fortifications. The extent of ancient Maya agriculture also stunned archaeologists, who said that the civilization produced food “on an almost industrial scale.”

And, as to the 'living in harmony and barely leaving a footprint' thing,
LiDAR was also used to reveal new details of the swampy valley around the Maya city of Holmul near Guatemala’s border with Belize. The LiDAR data show that the thousands of acres were drained, irrigated and converted into farmland, creating a landscape that archaeologists have compared to the central valley of California.

If the multiple universes theory is correct, then there may be one where some tribes figured out how to work and use iron; that would've put an interesting twist in what happened when the Europeans first arrived.