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.