Follow-up/Clarification question: Was there ever a time that they were declared "finished"? Was there a moment that the pharaoh (or whoever) said "all work is complete, we did it!" Or was it one of those projects that just kept being improved and upgraded until the pharaoh's death, and maybe even after?

im curious to know how many other empires knew about it and if they had plans to see it.

While I can't give you specifics on the celebrations of the pyramids, I can quote for you what an Egyptian celebration was like. I'm not sure if it will be of interest to you, but this sort of stuff fascinates me. :)

edit: This is a quote from Cleopatra: A Life, in which the author describes a Ptolemaic procession in the 3rd century BCE. It is sourced from The grand procession of Ptolemy Philadelphus.

Alexandria had long been a city of parades and pageantry, displays in which the wealth of the Ptolemies surpassed even the recreational fervor of their subjects. Centuries earlier a Dionysian procession had introduced gilded twenty-foot floats to the city streets, each requiring 180 men to coax it along. Purple-painted satyrs and gold garlanded nymphs followed, along with allegorical representations of kings, gods, cities, seasons. A center of mechanical marvels, Alexandria boasted automatic doors and hydraulic lifts, hidden treadmills and coin-operated machines. With invisible wires, siphons, pulleys, and magnets the Ptolemies could work miracles. Fires erupted and died down; lights flickered from statues’ eyes; trumpets blared spontaneously. For this early procession, the city’s ingenious metalworkers outdid themselves: a fifteen-foot tall statue in a yellow spangled tunic floated through the streets. She rose to her full height, poured offerings of milk, then magically reseated herself, enthralling the crowds. Around her the air was thick with the buzz of anticipation, the murmurs of admiration, the music of flutes. Clouds of incense—essentially moneyed air—settled on the spectators, for whom the burnished wonders continued: golden torch carriers, chests of frankincense and myrrh, gilded palm trees, grapevines, breastplates, shields, statues, basins, gold-adorned oxen. Atop one cart, sixty satyrs trampled grapes, singing as they did so, accompanied by pipers. Vast skins disgorged scented wine into the streets; the air was sweetened first by incense, again by those fragrant streams, a heady combination. Attendants released doves and pigeons over the course of the procession, each with ribbons dangling from its feet. A display of animals was obligatory for the subjects who had traveled to Alexandria and pitched tents for miles around. The third-century procession had included troops of decorated donkeys; elephants shod with gold embroidered slippers; teams of oxen, leopards, peacocks, enormous lions, an Ethiopian rhinoceros, ostriches, an albino bear, 2,400 dogs. Camels carried loads of saffron and cinnamon. Behind them paraded 200 bulls with gilded horns. Lyre players followed, along with 57,000 infantry and 23,000 cavalry in full armor.

This question might be better answered at /r/AskAnthropology.

Another question, what would happen to the slaves who helped build it? Would they have a surplus while building the pyramids?