The caverns are the end goal after you've found your mate, and they range in size from small to large to match your dino based on their diet (the small cave at the end can't be entered if you've eaten too much meat so you have to backtrack even further).
Yeah the health/hunger bar was just a quick and dirty solution, the script that sets the value stops running on death which is why the bar can be interacted with.
We meant to have more custom art but of our three artists only one actually found time to finish anything (just the volcano), so we had to ship with the placeholder assets.
I planned on having a slightly better tutorial but I injured my hand the other day which made it painful to work on the project for the last two days, so I just typed out a wall of text :(
Thanks for the feedback!