File:Vertical hole cave and weird thing.png

Summary
So ! I just started to play subnautica (I got the game this week-end), and I was exploring a little in creative to get more familiar with the game, and then I found this cave. Everything is writed on the picture, you you can't understand my handwriting, it's fine, you can ask in the comments. ^^ PS sorry for the pink-ish fuschia, it's the best color to see ._.

If someone know what exactly this thing is, please tell me ! I'm really curious about it ! ^^

EDIT : WOOPS ! I forgot to remove the .png at the end of the title and I don't know how to remove it... sorry "^^