Secrets of the Great Pyramid of Giza

Looming over desert sand on the bank of the River Nile, the 4,500-year old Great Pyramid of Giza is the only surviving relic of the Seven Wonders of the ancient world.

Yet despite being visited by millions of tourists every year, and poked and prodded by modern-day archaeologists armed with the latest robot technology, the giant monument - built over 20 years as a tomb for Egyptian pharaoh Khufu (known as Cheops in Greek) - still holds tightly onto many of its secrets.

Day-trippers from Cairo who brave long ticket queues, hawkers and ill-tempered camels to explore inside often complain that they are rewarded with little more than a guided tour of an ill-lit, cramped and overcrowded passageway.

But much of the vast structure remains out of bounds to the visiting public as work continues to reveal hidden doors, secret chambers and painted hieroglyphs which give a tantalising glimpse into the ancient world.

The Great Pyramid was built in around 2570BC by gangs of up to 200,000 peasant workers, slaves and engineers who between them raised six million tons of limestone and granite blocks - weighing 2 tons each - to an original height of 146 metres.

The oldest and largest of the three pyramids at Giza, it was the tallest building in the world until Lincoln Cathedral was completed in 1300, and while it has lost six metres to erosion over the millennia it remains a stunning monument to human endeavour.

Victorian explorers revived interest in unraveling the pyramid's many enigmas. Their enthusiastic, if amateurish, exploits have since been superseded by scientists working under the supervision and control of Egyptian authorities.

Theories abound from the outlandish (two copper fittings found at the end of a recently mapped tunnel are power-points for alien technology) to the prosaic (they are merely ornamental). Some claim that the mythical Hall of Records - a great library of hidden treasures - lies in catacombs which riddle the ground below.

The most recent exploration - named the Djedi project after a mystic apparently consulted by the pyramid's original architects - was led by a team from Leeds. They used a bendy "micro-snake" camera that can see around corners to examine two mysterious shafts which lead from one of the three burial chambers to highly-polished stone doors. Images sent back revealed hieroglyphs written in red paint and unexplained lines scratched into the stone.

Zahi Hawass, Egypt’s Minister of State for Antiquities Affairs, described the doors as the pyramid's "last great mystery" hinting that they could lead to a secret room which has remained hidden for thousands of years.

But the Djedi team's research was halted by the civil unrest which led to the fall of President Hosni Mubarak last year and, with the political situation still hanging in the balance, their full findings have yet to be released.

In conspiracy-thriller ‘The Da Vinci Code’, Dan Brown's character Robert Langdon wondered aloud "if any of Harvard's revered Egyptologists had ever knocked on the door of a pyramid and expected an answer”.

Egypt must resolve its own modern-day political tangle before he, and the rest of the world, can finally find out.