The Chamber of Darkness is an underground location on Eternia that features in He-Man and the Masters of the Universe.
The Chamber of Darkness was an underground prison where Darkdream had been imprisonned some time after attacking the Royal Palace. It was located near the Crimson Valley.
The chamber featured a sylized throne for Darkdream, which may impy that he had used it as his base of operations before being cut off from the surface world and being unable to use his powers of nightmare on the people of Eternia.
When mysterious explosions caused by the dangerous mineral Nodroxyn weakened the seal on the Chamber of Darkness enough to allow Darkdream to use his nightmare powers once again. He contacted Tavor and Evil-Lyn to blanket the planet in everlasting darkness so that he could thrive and go outside. In his eagerness for power, he pressured his minions to move one of Eternia's moons to create a solar eclipse, but the instability of this magic caused the moon to fall towards Eternia. When He-Man averted the collision, daylight returned to Eternia, and Darkdream was defeated once again.