Hello!
The Void Octopus on the beach you can interact with, will have a heart above it. The beach one will appear once you find the first one, Located at the Storage room of the The Void's Tavern. It has no requirements, but you do need to figure out to approach it correctly to trigger the scene.
And dang!!! You found that FAST! The spooky dungeon is a mini game that connects to something big in a near future. Little clues are here and there with different NPCs and locations. The event you saw (Which I'm guessing you found the empty dungeon instance) Is a very rare event that has some very specific circumstances to be triggered. I'm surprised it was found that fast. It's working as intended, but no, currently, it is not complete. With each update, I plan to add more to it which will not be in the patch notes. Happy hunting!💖