This is my recreation of the photo the devs tooks, but with a compass

Rough coordinates: 1326:33:17



This should give you a better idea of which biomes are near.



It is behind this rock, north of the aluminum mining / rock mushroom area

Even though the event has ended, the area is still in the game with some furniture, can be accessed if you put a teleporter there before the event ended.

I do have the most recent development update to the game, specifically the Volcanic update:



Previously, I had left both a teleporter and a ladder in the event area to go back to just for fun to access the now "hidden" area.




As you can see, now that teleporter only brings you to an empty area under the map. The room and its furniture have been removed from the updated game. I waited 5 minutes to see if it was just my old computer lagging in rendering the area, to make sure. (NOTE: I have development mode on in the steam beta section, it may still be there if you are not in development mode, that I do not know).



Thank you to BlueJagger, in the comments for asking.