Fodor's Expert Review Unfinished Obelisk

High-quality granite from Aswan is used in temples, monuments, and obelisks across Egypt, and this failed extraction was instrumental in figuring out exactly how the ancients cut such huge pieces of stone from the quarry. The stonemasons discovered a flaw in this massive obelisk-to-be, and it was left imprisoned in the bedrock. Had it been raised, it would have stood 42 meters (138 feet) tall—larger than any other obelisk—and weighed 1,168 tons. 

This site is often included on Aswan tour group itineraries, but unless you're particularly interested in ancient stonework, save your precious vacation time for more interesting sites.