From this emerges a sub-theory I came up with, regarding a potential sea monster—possibly the Unagi (the creature from *ATLA* that swam near Kyoshi Island).
Additionally, we can see the concept art from this month's NYCC, the creators noted that this is one of seven havens, built upon the skeleton of a monster. In my opinion, this is a large sea creature that once swam in Chameleon Bay, and the shelter was constructed on top of it.