There’s something unusual going on inside the Great Pyramid of Giza. An international project by scientists and architects to scan four Egyptian pyramids with thermal imaging technology has turned up several anomalies that indicate that there may be more to the structures than previously realized. 

The creatively named Operation Scan Pyramids is gathering thermal imaging data on Giza’s Pyramid of Khufu (the Great Pyramid) and the Pyramid of Khafre (Khufu’s son), and two pyramids built in Dahshur by Khufu’s father, the 4th Dynasty ruler Snefru. After two weeks, the thermal scans have turned up several unusual patterns that were observed on all the pyramids, including one “impressive” anomaly on the Great Pyramid: some of the blocks of the limestone structures are hotter than others. 

To an outsider, this might not seem like a big deal, but experts say the difference in heat could be caused by internal air currents—or unknown chambers within the pyramids. The project is expected to continue until late 2016, and architects and researchers will no doubt be poking around in the possible voids in the structures to determine what exactly is causing the temperature difference. 

[h/t: The Guardian]