The Shadow Gate

The most mysterious of all the artefacts, the Shadow Gate is a circular half sphere within a stone arch, made of a material never seen before. Only one of these devices have been found, and it was found alongside a strange pedestal with six rectangular indentations. It is thought to be some sort of portal, and that the pedestal is used to activate it somehow. It was found within a ruined chamber several hundred feet beneath the sands of Almahna, beneath Calrune, in the old city.
The indentations in the pedestal were later found to fit strange stone cards found in various places around the world. Each stone card, called a Symbol Stone, has a different symbol carved upon it. They are the keys which activate the device. However, only three have been found thus far, and when placed upon the pedestal in various combinations, there is a slight rumble but the device does nothing. It is thought that six are needed, to fill all six indentations in the pedestal.
In ancient times, when the Alchemists came to the decision to leave this world, they also decided that none should follow them unless they could prove themselves worthy by learning for themselves the secrets of the device. And so they sealed the Shadow Gate chamber behind them and left behind two of their own who, upon the departure of the others, would scatter all the Symbol Stones to the far corners of the world. There were ninety-nine in all.
The truth of the Shadow Gate is stranger than fiction. It is true that it is a portal. But not just any portal. It is a gateway to millions of different worlds across the multiverse. Over the ages it has fallen into disarray. The professors of the Academy of Almahna did what they could to repair it, but they still can not get it to work.
Recently, in 2743 3A, more of these devices have been discovered, buried in various places through out the world.

Summary

These devices are also known in the ancient tongue as Ouboros.