Since I saw that video of someone filming the island from a boat and the pictures of that blue tent below the weird temple, I convinced myself that there could be underground shit there.

I found Apple's Maps has very good imagery of the island. The island is even 3D "modeled" so you can get a better sense of heights.

The island

At first I suspected that small white thing beside the bigger white "tent".It kinda looks like an entrance.

Suspicious white tent

Then I looked around and BAM! Look at this!

Underground 1

Underground 2

Undeniably there are underground spaces on that island. What is that underground space for? What size is it?