How come you don't know this already? If you have some notion aliens had to be involved because the task was too difficult for humans, the only reasonable way to come to that conclusion is to have studied the accepted method of construction in detail. You should then know that stone and copper tools were used by the masons of the age. But of course, this still doesn't answer why you single out the construction on the pyramids as being extraordinary, when you don't question the pillaging of the giant obelisks and their removal to other countries, by ancient Romans etc. Or why you don't marvel at the construction of Lincoln Cathedral, which became the largest structure on Earth, surpassing the Great Pyramid. Here's a picture from the inside of Lincoln Cathedral:
And the ascent inside the Great Pyramid to the burial chamber:
So, understand this,... the Cathedral is taller, and more decorative, a more complex shape, with bigger expanses than the Egyptians could engineer (go to Karnak and see how close the columns are together, then see the majesty of the vaulted arches in Lincoln). But you doubt humans could pile up a bunch of blocks, and smooth the outer and inner layers? But it's achievable to make vaulted arches, using no more than wooden scaffolds and rope? Don't get me wrong, the Great Pyramid is impressive, but simply because it is big. Visiting it, you understand the sheer effort it took to create, but it's not actually that complex.