The Mystic Portal, is thousands of years old. Built during the time of the Acient World, it was meant to harness the mysterious power of Canyon Myst. The inhabitants, both human and fae, had an advanced culture that explored the oceans, geothermal power, and time travel. A temple was erected around the portal, and those who sought to experience future or past worlds would make the one way committment to step through to another time. The ancients carved a map of destinations in rune symbols, that aligned to the timing of tides. They discovered the ocean dictated the forward and backward outcomes of the portal, and where the travelers would go--future or past. As the tide moved, the runes would align, shifting in fluid motion even though carved in solid rock.
The leaps in time were governed by laws beyond comprehension, to ensure a paradox could not occur. A traveler would arrive in the same physical space, but hundreds if not thousands of years had passed in either direction. Additionally, once through the portal, it would never reveal it's power to the traveler again. The rune map provided a way to predict or program the destination. Based on the runes described in the Mystic Portal, there was further development of the portal after the cataclysm, showing time before and after the great volcano erupted.