The Estorian Hourglass was a magical hourglass created by magical researchers at The Ziggurat using the Tear of Boccob. It has the power to alter the flow of time, allowing the user to move faster or slower as they desire, or even reverse time briefly. The true extent of its powers are unknown, as the sand that powers it can only be replenished with the death of a powerful creature from one of the Outer Planes. When such a creature dies within close proximity of the hourglass, the artifact will - of its own volition and by unknown means - obliterate the creature's physical remains and absorb them into itself as a small quantity of sand.
The Estorian Hourglass's first known use was in 2145, when it was used to reverse time and prevent the traitorous researcher Kask from using the Tear of Boccob to destroy the other researchers. It is unknown what uses it was put to thereafter, but the Challengers of the Unspeakable found it in the Ziggurat in 2959 and took it with them. It was carried by Kayleth Lifesinger for a time, until she fell into the Abyss. It is unknown whether the bard still had it in her possession when she returned to the Material Plane, or whether it was lost in the realm of the demon lord Oublivae.