[Havoc]

>why you'd put some parts of your estate underground

My question was more about the specific combination of 1) underground 2) in each corner.

I can come up with a plausible reason for either, but not in combination

[bflesch]

I guess it's storage, sensors and microwave links. On one corner you can see a concrete pad where a small boat can land unseen from the mainland. There are some official helicopter flyby videos but all of them fail to capture this one particular side of the island.

It's like a CIA naval base for drug smuggling.