The Great Pyramid, the tomb of king Khufu, with its original height of 146.5 meters, was the tallest structure in the world for 3,800 years. It remains the last surviving member of the Seven Wonders of the Ancient World, and took an estimated to 10 to 20 years to build. To this day, it is not entirely certain how this was done. The Great Pyramid is made of local limestone, but its exterior was once entirely covered with high quality limestone. These casing stones were brought from Tura, south of Maadi, by ship. On the inside, the pyramid has three chambers, one cut into the bedrock underneath, and two high up within the masonry itself, a feature that no other pyramid possesses. The sarcophagus in which Khufu was once laid to rest can still be seen in the upper of these two rooms, the King's Chamber. This room is accessed through the Grand Gallery, a majestic corbelled ascending passage, and a masterpiece of ancient engineering and architecture. Two large and impressive ships were discovered in pits on the south side of the pyramid in a dismantled state. These are believed to have been used to transport the royal mummy and burial equipment to the tomb.