Cave with Air *spoiler?*

[Doc Brown]

hello you,
last night i installed subnautica - and im realy impressed of the game! but long story short: after 2 h of playing i drive with my seamoth into the direction of the grand reef. on the cliff at around 130 m i find a hole. im was a little bit scared but i dive into this cave. there are many ways with stalagmites in this cave, also i found a purple card/whatever on the ground bye the entrance. deeper in this hole i found air, i get out of my seamoth and walk a little around. but i dont have any light or water with me, it was late and as i say, i was scared as hell at this point.

today i check youtube if i can find any video of this cave with the under-water island/airbubble/whatever, but i found: nothing. so, what is it for a place? i will go and search it tonight again, sith some light and more water with me.

[Xautos]

you probably found one of those alien arch cache locations, a forcefield holds the water back but allows you to go through. you need to activate an alien arch elsewhere on the planet in order for the arch in the cache to work.

spoiler below:
Primary containment facility

[Doc Brown]

no forcefield or somthing, just a realy small way, just bigh enough for my seamoth, goes deep into the cliff and ends in a big cave with air and some ways deeper in the cave. but without light i had no chance. in this cave i dont found any alienstuff exept the card in the entrance.

[DeFragged]

If you found purple alien tablets, you're on an island with a cave system that comes up into a cavern with air.