Legend,
Are you saying that the entrance sealed with what you described as black cement is located near the water and at high tide, it is submerge in water and that means you can only work during low tide and of course you are constantly pumping out water from your hole, that is a job and a half. How did you ever find out about this site, was there a map or a marker or a live pointer that pointed out this location, on water. You stated that you already broke the seal that leads to a tunnel with chambers, what is on those chambers. For the Japanese to go to that much extreme, hard to imagine the difficulty of tunneling, unless the tunnel was natural and they only have to seal it, that would be the natural deduction. Am asking all this questions for me to better understand the way the Japanese hid their loot.