Shattered Mirror

The Large Prismic Black Monolith (known by the Great Beings as the Shattered Mirror) was a device created by a dying Great Being named Okk. It allowed for travel between the Original Universe and another universe that henceforth became known as the Shattered Mirror Universe. It was indestructible as it was a fixed point in time and space, until wibbly-wobbly timey-wimey stuff happened and it went kaput.

History
In 33,075 CMT, the Architect enlisted a dying Great Being named Okk to create the Shattered Mirror in response to Blackout's gained knowledge of the Users. Okk died shortly after completing his creation.

At some point, the Shattered Mirror was transferred to the Shattered Mirror Universe's version of the Metru Nui Archives, where Kakamu and Ta'harok entered it in a plan to travel to the Original Universe. When Kakamu's second-in-command, Ynot, discovered what had happened to Kakamu, he had the Shattered Mirror brought to Destral so that he could study it further. There, Ynot discovered the Shattered Mirror's true function and deduced that it had taken Kakamu to another universe. Ynot was able to use the device for short intervals; not nearly long enough to pass through, but long enough to discover many things about the universe it led to. Ynot eventually launched the Shattered Mirror at the black hole that had consumed Chenrotoss in an attempt to prevent Kakamu's return, but the device instead ended up in the corresponding location in the Original Universe, where Kakamu and Ta'harok emerged onto that universe's Chenrotoss.

Over time, many more characters used the Shattered Mirror to cross over into the Original Universe, including Muta, who promptly crashed into an asteroid, and Teridax, who went to stop Naju from reaching Atlantis.

Eventually, the Shattered Mirror appeared on the same planet as Atlantis, where some of SM Trantoshen's minions came through, grabbed Trantoshen, and took him back to the Shattered Mirror Universe so that he could help SMT to stop SMY from supposedly conquering the universe with a new superweapon. However, this was a trick to get Trantoshen to help him in his eventually-successful attempt to take over Destral.

After the Shattered Mirror was destroyed by temporal shenanigans, SM Trantoshen spent a year building a successor, the Shattered Mirror II, as a means of gaining access to the Original Universe once more.