Thermal scans of the Great Pyramid of Giza have revealed an "impressive" anomaly in the rock -- a change in temperature that could indicate something behind the 4,500-year-old walls. "This anomaly is really quite impressive and it’s just in front of us, at the ground level," said Mehdi Tayoubi, founder of the Paris-based Heritage Innovation Preservation Institute that is conducting the Scan Pyramids experiments using a mix of infrared thermography, muon radiography and 3D reconstruction. The anomaly is located on the eastern side of the pyramid, also known as the pyramid of Khufu, as can be seen in this image provided by the organization: The scans were conducted at different times of the day and night; temperatures were measured as the stones grew warmer and cooled off.