The Great Pyramid at Giza
The oldest of the Seven Wonders is located on the Giza plateau, West of modern day Cairo. According to Herodotus, who visited Egypt in 450BC, the Great Pyramid was built in 20 years by 100,000 slaves. He was also told the construction had been done by huge machines that lifted the stones in place.
Now remember the pyramid at this time was over 2000 years old at this time, so it's likely the exact building techniques had been forgotten. Then again, he was told (correctly) the building was created to house the remains of Pharaoh Khufu, whom the Greeks called Cheops, so maybe the time it had taken and the number of workers was correct. Modern archeologist seem think the construction was done by free peasants rather than by slaves and indeed records have been found of these pyramid workers going on strike because they didn't get any onions.
The pyramid, with its height of 144 meter, was the highest building on the globe until someone decided to build the Empire State Building in New York. The pyramid has a base of 225 meters and consists of some 2.3 million blocks of stone. The blocks average 2,500 kilograms in weight and are thought to have been moved up wards on ramps of sand that were build around the pyramid.
Khufu's tomb is place nicely along the compass points and the measurements seem to be accurate within inches. This accuracy, that could never be achieved by pagans, read heavy sarcasm here, has given rise to wonderful theories involving alien races and flying saucers.
The Pharaoh was buried here with many a grave gift, however, non of these remain. Actually, nobody has found much evidence as to who the pyramid was for anyway, except for one inscription that suggests Khufu.
In 820AD Abdullah Al Manum put a team together to dig for the treasure. The discovered various rooms and corridors, some blocked by granite plugs, but no trace of a treasure. They did find a very large granite sarcophagus, but the room they found it in was as bare the rest of the pyramid.
After this useless exercise, the Arabs used the Tura limestone cover of the pyramid to build Cairo. They also tried to use the rest of the pyramid, but never got further as taking apart the top 10 meters.
In 1638 John Greaves, an English mathematician explored the pyramid and found an additional passage, which he claimed was used to tale away the treasure. The corridor is rather narrow and it seems unlikely to be big enough to have allowed for something like the sarcophagus' lid.
By now some people think the pyramid was never used as a tomb, one of the alternative uses that they propose is the one suggested by the Roman author Proclus: it was used as an astronomical observatory. Others are using this theory to suggest the pyramid is a lot older than 4500 years because the found the passages align to stars and constellation that could only have been visible more than 10,000 years ago. The pyramid, part of a group of three, has also been seen as part of a mapping of the constellation of Osiris (Orion), with these three making up the belt. They even discovered a new pyramid in a place where it fits the constellation.
Curiously enough, the sky map it should represent is also about 10,000 years old.
Other people are still trying to find additional rooms in the pyramid, in the hope of proving once and for all it really is a tomb.
Perhaps we'll never know what it was used for but whatever way you look at it, it's still one of the most impressive monuments on Earth.
Other sights at Giza.