The Temporal Obelisk

The Temporal Obelisk is a structure built millennia ago during the Primal Age. Some say that it was built by the Celestials themselves, while others say that it was the word of powerful wizards. Regardless of your belief, the power behind it cannot be understated.

Purpose / Function

To alter the threads of time and reality.

Defenses

Magical barriers were put up around the Temporal Obelisk, making it so none but either the most powerful of mages, or those allowed by the Celestials themselves, were allowed into it. It is as if an impervious bubble, resistant to even the strongest spells, is in place around it, preventing anything from getting in or out.
A single guardian also exists within the confines of the shield, present to ensure the sanctuary that the obelisk has become to those with knowledge of it. It will dispatch any who dare try to pervert its magic or attempt to harm others without a second thought.

History

During the Primal Age, the Celestials were much closer to the Material Plane, able to influence it much more readily. They gave gifts to the mortals under their care so that they may go forth and protect themselves, spread their will, and destroy that which threatened their way of life. Some of those in their charge implored their gods to allow them to experience time slower if they needed to accomplish something that would otherwise take lifetimes but had naught but a few days. Others wanted to quickly see the rise and and fall of civilizations. And so, in conjunction with some of the most powerful wizards of the day, they created the Temporal Obelisk.
It is about fifteen feet tall, made of dark grey, cubic stones stacked atop one another, each etched with different colored symbols. The different stones are able to turn, allowing those who interact with it to create different patterns on the faces of the obelisk.
The Temporal Obelisk has unique powers on Lumarvis -- powers never seen before or since. By turning the stones, one can alter the flow of time for those within the bubble. It can speed it up, allowing you to find yourself jumping days, weeks, months, years, or even centuries ahead in time. Or, it can slow it down, allowing you to live out an entire lifetime in the span of a couple hours. Regardless, the bubble that was put in place around the obelisk creates a unique dimension -- one very close to the Material Plane -- for those who activate it. It is able to create hundreds, even thousands, of these side dimensions, one for each person who uses it. There is no telling when someone might magically appear, walking out of it. In the same thread, you never know when you'll see your friend that walked into it. Perhaps it will be a few minutes. Perhaps you will be long gone by the time they return. There is no telling, and some who activate the obelisk instantly grow to regret it when they have seen a thousand years pass by in the blink of an eye.