One of the great mysterious monuments is Great Pyramid of Giza in EGYPT. 4600 years later after it is built, it is still one of the largest monument in earth. It was built as a tomb for pharaoh named Khufu. 2.3 million stone blocks each weighs 2.5 tons are placed with unbelievable precision to built great pyramid of Giza. Four sides of pyramid are aligned to east, west, north and south direction.
There are two shafts inside the pyramid, one to the north and one to the south. It is believed they were built to observe two celestial events.
Today these shafts don't line up to any stars. But about 5000 years ago when this pyramid was built north shaft pointed to North Star and the south shaft pointed to the center star of Orion Belt. The shafts don't point those stars today because earth completes a cycle, where tilt of its axis changes in 23000 years.