Sumerian tablet describes a sealed gate in Dilmun which is now underwater, which is due to reopen on a timer in the near future.

They found the gate because the Sumerians used star constellations instead of lat / long. In this case it's oriented around the Pleiades.

The obsidian gate has a symbol of seven circles and a point in the centre, which represents the seven levels of the underworld.

We see the same symbol in Ireland among other places.

https://youtu.be/nB7R9f8oyUU