Researchers in Egypt using advanced scanning techniques to study the Pyramids said this week that they had detected “thermal anomalies” within the Great Pyramid of Giza that could indicate the presence of an undiscovered tomb.

That is one possible explanation for striking differences in temperature that the multinational research team said it found between the stones at ground level on the eastern side of the 4,500-year-old structure, according to Egypt’s Ministry of Antiquities.

“The first row of the pyramid’s stones are all uniform, then we come here and find that there’s a difference in the formation,” Mamdouh el-Damaty, the Egyptian minister of antiquities, said to journalists on Monday, according to The Associated Press.

He said the team found “that there is something like a small passage in the ground that you can see, leading up to the pyramids ground, reaching an area with a different temperature. What will be behind it?”