Its only use is to have an Ancient Key to be placed in its socket, making the Atrium's Nightmare Cycle be locked at the peak state. It can be removed again, unlocking the Cycle from its peak. If a fully-constructed Odd Skeleton is revived near an activated Ancient Gateway, the fight against the Ancient Fuelweaver will begin. The Ancient Fuelweaver can deactivate the Atrium's Nightmare Cycle by removing the Ancient Key. If the Ancient Fuelweaver is killed it will trigger an explosion that will activate after three minutes, renewing the Ruins. Twenty days later, the Gateway will accept the Ancient Key to be placed again.
In the the Heart of the RuinsPart 1, when examining an ancient gateway with a key inserted into it, the character said: "The lights reveals ancient text: Come Back Next Update."
When first released, the Ancient Gateway had Black and Yellow tapes all over it, to signalize it was still a work in progress feature.
WX-78's quotes, "ERROR 502" references the actual Error 502 which means "bad gateway error".
The work in progress visual of the Ancient Gateway
Gateway after the Ancient Fuelweaver dies
The Gateway exploding.
After the explosions.
The Ancient Gateway, as seen in the What Lies Beyond? video clip.