Egypt is home to the most famous pyramids of all, three well-formed examples located at Giza on the outskirts of Cairo. Just as there are pyramids throughout the world, it should come as no surprise that Egypt has more than just these three. Egyptologists have actually catalogued over 90 major pyramids that were built over the course of 1,000 years (roughly 2600-1550 BC).
All the pyramids can be found close to the west bank (none on the east bank) of the Nile, with the majority found along a 17-kilometre stretch incorporating Abu Ghurob, Saqqara and Dashur. Giza is 11 kilometres further north. Because of their size and relative proximity, when visiting a site it is quite normal to see other pyramids on the horizon.
Although each Egyptian pyramid has individual features, they are far more alike than houses in our modern suburban streets. The shape we know. The heights range from 17 to 146 metres, with the faces at an angle to the base of 42-57 degrees, with a couple of 18 metre pyramids attaining more than 70 degrees.
The largest pyramids were built in quick succession:
"The truly gigantic stone pyramids were built over the course of only three generations: Sneferu, Khufu and Khafre. If Sneferu did indeed build the Meidum pyramid as well as his two stone pyramids at Dashur, his pyramids alone contain more than 3.5 million cu. m (124 million cu ft.) of stone. All the other pyramids of Egyptian kings combined (excluding queens' and other satellite pyramids) contain only 41 per cent of the total mass of the pyramids of Sneferu, his son Khufu and grandson Khafre." 
It makes sense, on first impressions, to label these pyramids as gigantic mausoleums for deceased pharaohs. They typically contain secret entrances and passages, some which lead to rooms underneath the pyramid, and some that just come to an abrupt dead-end. The main rooms have stress-relieving chambers above them - to stop the immense weight crushing down and destroying whatever was in the room. These rooms have contained sarcophagi, but never with a body still within, which has prompted alternative researchers to look for other, non-burial purposes for these structures. Some sarcophagi were even found closed and sealed, yet still empty!
Ancient Egyptian texts have mentioned 80 men being required to set the lid on a stone sarcophagus. This is in keeping with the overall immensity of size and weight. The pyramids represent inconceivable size and unbearable weight. To my thinking they represent the scale between the ordinary and the incredible, between a simple burial chamber and a pyramid, between a standard earthquake or hurricane and a global cataclysm.
In close proximity to the major pyramids, there are usually temples and/or satellite pyramids - miniatures commonly known as Queens' pyramids. These can also contain passages and chambers.
The Great Pyramid of Cheops/Khufu
The pharaoh Khufu reigned for 23 years from 2789 to 2767 BC, and it is the accepted orthodox view that he constructed the Great Pyramid as his personal tomb. However, the pharaoh's body was not found within it, nor any treasure, or anything remotely related to a funeral. No mummy has ever been found in a pyramid in Egypt. Mummies have always come from mastabas or tombs in the Valley of the Kings.
Independent researchers have come up with an array of alternative dates for the construction of the Giza pyramids. But if we rule out the endless possibilities of inter-galactic visitors, there are no solid theories as to who else could possibly have made them.
The Great Pyramid is huge. Its base covers 13.6 acres and for its weight estimates vary between 5.75 - 6.5 million tons, based on 2.3 - 2.6 million blocks.  Napoleon's surveyors calculated that the three Giza pyramids contained so much stone that they could build a three metres high by one metre thick wall around the perimeter of France with it.
The pyramid is located at 29 degrees, 58 minutes, 51.06 seconds north latitude, and 31 degrees, 9 minutes, and 0.0 seconds east longitude. This is very close to 30 degrees north, and it has been suggested that the Giza Plateau was the best spot to place such an immense weight, whereas other areas would not be able to cope.  The line of 30 degrees latitude is only a mile or two the north, so they may have thought it was the best they could do, short of building an unstable pyramid that might not last the required millennia.
Some believe that Giza is a special location that is at the centre of the earth's land mass. If you follow the east/west parallel around the globe, it crosses more land than any other parallel. The same goes for the north/south meridian that intersects with Giza. These two lines also cross in the ocean.
Although there appears to be more land along the Russia / Alaska parallel, if you use a globe this illusion disappears.
Much has been made of the extreme accuracy of the Great Pyramid's alignment to north, with less than 1/15 of one degree of error.  However, this might be the least remarkable feature, when you consider the math that has been built into it (see below).
The top of the two giant pyramids are at the same height, although the Great Pyramid is actually larger because its base is lower. A lot of effort was put into creating this effect:
"the base of Khufu's pyramid is level to within just 2.1 cm.in building the pyramids of Khufu and Khafre the ancient masons started on a sloping plateau c. 7-10 m (23-33 ft) higher than the eventual base and in each case left a massif of rock in the body of the pyramid" 
It is hard enough to fathom why this design aspect was so important in Giza, without considering that in Teotihuacan, Mexico they did the same thing with their Pyramids of the Sun and Moon.
Another feature which is rarely mentioned is that the four faces of the pyramid are slightly concave, a feature probably unduplicated anywhere else, ever. Some say that this curvature is the same as the earth itself, which would add weight to ideas regarding the pyramid as a model of our planet.
The centre of each side is indented to form an eight-sided pyramid. The effect is not visible from the ground or from a distance but only from the air, and then only under the proper lighting conditions. 
The measurement used in the construction of the pyramid is known as the pyramid inch "PI". It is equal to 1.0011 modern inches. Twenty-five pyramid inches made up one "Sacred Cubit".
The perimeter of the pyramid's base divided by twice its height equals "pi" to 5 decimal places:
9131*4 / 5813*2 = 3.141579+
The dimensions used are pyramid inches, but because this is a ratio, any form of measurement will give the same result. In this way it is future proof, in that alien beings could arrive and inspect it thousands of years from now, and still derive pi.
What makes this extraordinary is what is required to make this ratio occur - the slope of the pyramid's sides needs to be precisely 51 degrees, 51 minutes, and 14.3 seconds. Of the 90 major pyramids in Egypt, the Great pyramid of Giza is the only one with this angle.
The perimeter of the base is equal to the calendar year - 365.24 pyramid cubits
Many, many other equations have been discovered, with dozens of books consisting of not much more than pyramid numbers. Some are ridiculous, and most are hard to prove without a single, definitive source of measurements. Many are so complicated that they appear contrived.
By focussing on the few definites - location, size, angle and alignment, we can be certain that someone, long ago, was trying to impress upon us that they knew things. They wanted our attention.
You've probably heard of the biblical Tower of Babel. The word "Babel", in its original Akkadian language means "the gate to god". In Mesopotamia attempts to recreate the Tower of Babel were known as ziggurats - man-made mountains with a shrine at the top.
A ziggurat is a pyramidal, stepped temple tower. characteristic of the major cities of Mesopotamia (now in Iraq) from about 2200 until 500 BC. The ziggurat was always built with a core of mud brick and an exterior covered with baked brick. It had no internal chambers and was usually square or rectangular, averaging either 170 feet square or 125 170 feet (40 50 metres) at the base. Approximately 25 ziggurats are known, being equally divided in number among Sumer, Babylonia, and Assyria.
No ziggurat is preserved to its original height. Ascent was by an exterior triple stairway or by a spiral ramp, but for almost half of the known ziggurats, no means of ascent has been discovered. The sloping sides and terraces were often landscaped with trees and shrubs (hence the Hanging Gardens of Babylon). The best-preserved ziggurat is at Ur. The largest, at Chogha Zanbil in Elam, is 335 feet (102 m) square and 80 feet (24 m) high and stands at less than half its estimated original height. The legendary Tower of Babel has been popularly associated with the ziggurat of the great temple of Marduk in Babylon. 
As you can see from the photos, ziggurats do not have the geometric beauty of their cousins the pyramids. Yet, when broken down to components, they are very similar - religious purpose (typically there was a shrine at the summit), gigantic size, stepped and stair cased. They are also very old - the Ur ziggurat dates to the 25th century BC, making it contemporaneous with the Giza pyramids. Therefore I feel that they belong in our studies of pyramids and their purpose.
TurkeyMt Nemrut, Kâhta is a natural mountain (2150m), with a 50 metre artificial peak built on top. It was constructed as a tomb for King Antinochus I during the period 80 B.C-72 B.C. If pyramids are meant to represent mountains, the builders of this one have gone a step further by placing it on top of a real mountain.
Not just an artificial mound, this site features huge (10 metre high) statues.