Have you caught the show Ancient Aliens on the History Channel? Of course, most folks, including myself would immediately start picking apart the alleged "evidence" and hypotheticals. But, I found it even more fun to run with the premise.
There are those who believe that aliens from another world helped in the construction of the pyramids. In fact, they speculate that the pyramids and many obelisks were actually power generation devices, used to send power to the mother ship, orbiting the Earth. They employed humans to build and maintain these devices, until they had the power they needed, and left.
Suspend your disbelief for a moment and let's just say it's all the absolute truth. Before you get all excited about joining the "brotherhood of planets" consider what that means. Some ship from another planet was traveling in our neighborhood and ran low on fuel. So they stop by the Earth, employ the indigenous hairless apes to produce enough energy for them to top off their tank, and they go on their merry way. Obviously they had no qualms about exposing themselves to the natives, so the fact that they haven't been back can only mean, they see no reason to come back. Even if they did return, they'd soon discover that we didn't even bother to write down any of the great technology they shared, making a third trip to our humble abode even less likely.
So, if the scenario they've laid out is factual, it only proves that among advanced civilizations in the cosmos, we are perhaps the least interesting in the eyes of the rest. But don't fret. The only real valid points made in the documentary were that no one has yet figured out how engineers thousands of years ago could have made the precision cuts and engravings they made and that they haven't found a good explanation for some of the features of the pyramids. It couldn't possibly be that an engineer that lived thousands of years ago might have had some knowledge that today's engineers don't have? Could it? Nah, must have been aliens.