Area beneath the Grand Reef

[Sammyrism]

While searching for the Lost River, I came across what I thought was what I was looking for. However, after a while of jumping around the area with the PRAWN, I couldn't find any other ways to go other than one that lead to a big room with a skull-like structure being lit up by alien lights. On one of the walls, there is a closed alien door, like the ones you open with the purple artifacts on the northern island alien base.

What is this room, and how do you open the alien gate?

[Cougarific]

You can watch this if you want to - skip to 18:30 to see inside the room. Skip back to 8:30 if you want to see where I got the Alien Artifact to open that door.
http://steamcommunity.com/sharedfiles/filedetails/?id=877264357

[straykaiya]

You were in the lost river. That skull structure lit up by alien lights with a shielded door. That is in the lost river area. The "lost river" is the light green mist all over the floor in that area.

[straykaiya]

On a side note. Some people may not have realized either. Is, unless the devs change it. That room has a hole in the cieling, that leads directly to the blood kelp area and straight up to the surface.

[GlassDeviant]

It's just a cache of ion cubes, but you need a different coloured key for it. You find it down there, somewhere...not too far away but not particularly close. Hint: Follow Marguerite.

[Sammyrism]

Originally posted by Cougarific:

You can watch this if you want to - skip to 18:30 to see inside the room. Skip back to 8:30 if you want to see where I got the Alien Artifact to open that door.
http://steamcommunity.com/sharedfiles/filedetails/?id=877264357

I'll check it out, thank you!

Originally posted by straykaiya:

You were in the lost river.

Aha, so it was actually the lost river. I couldn't find anything on that skull room, just the area with the Emperor skeleton. Thanks for letting me know!