[SpookyZalost]

@Darth-Apple honestly I nearly died several times to drowning, there's a reason it's near the cliff wall, I had to make a sort of diving bell to use for air while I was working, place half a dozen blocks, get air, repeat.
once I built the structure I filled it in and then dug it out.

for the tunnels I gave some sponges a try, will admit, this makes things a lot easier, then just cook the sponges after to dry them out, rinse repeat.

once you get the hang of it, it isn't too bad, just takes longer.

once my friend comes back online though another day I'm going to make obsidian from the lava waterfall I found nearby and mount an expedition to the nether to gather netherwart for farming.

with nether wart and puffer fish I can make a water breathing potion that lasts up to 3 min, this would make things a lot easier for building underwater and I wouldn't need to return to the diving bell until it runs out.

to build a dome twice that size I'd need maybe half a dozen potions though.

lotta fishing.