Gantenbrink's Door is a stone block found at the end of a shaft in the Great Pyramid of Cheops. It is actually a dead-end wall, but it resembles an entrance-way due to two ornamental copper fixtures. Some conspiracy theorists have suggested that it is, in fact, a door, and have made wild speculations about what lies on the "other side" and who wants to keep it secret.

The shaft is located on the southern side of the Queen's Chamber--another inaccurate name, as there's no evidence it was ever used for Cheops' queen. The stone block is named after robotic engineer Rudolph Gantenbrink, who was hired to install ventilation fans in the pyramid. In 1993, he convinced the Egyptian government to allow him to send a small robot up the 213-foot shaft for exploration purposes, discovering only the wall that would soon bear his name.