We didn’t do the dive helmet trip, but on our own private charter, we asked to go to the same site. Yes, there’s a sunken pier, small sub, helicopter, and the old Heineken plane( which broke apart since last year) I took a vid and some pics in this link below.

With a few breaths, I could snorkel down. But if you really want to explore, I’d definitely do the helmets or scuba.

Vid and pics here