What to build?

 I sort of felt like my train track was a pretty epic project. It had demanded tons of my time, and I was left with something pretty amazing and functional. No longer would I have to spend an entire Minecraft day walking to my floating castle. But because it had been so great, it left me wondering what to do next. So I decided on a glass tower in the ocean. I figured it could also serve as a fast and not-confusing entrance to my most valuable mine. So I went downstairs to one of the largest chambers and started tunneling up. I figured it was under the water because of all the waterfalls. I was pretty confident I'm come up under the ocean but I wasn't worried about drowning. I was absolutely right to not worry about drowning. I didn't realize I'd come up under sand and be buried alive. Harumph.
At this point I figured it would be best to tunnel from the top down. I tried my best to figure out where my tunnel was going to come up, and this was what I decided. This tiny stone marker 10 feet off the beach.

When I was out there putting up the marker, I discovered I was a little off. There was a hole in the sand nearby... which is obviously where the sand collapsed on me. So I built a well.

And then I enlarge the well

And then I replaced the stone walls with Glass

That seemed time consuming... and the end result was the base of a tower not far from the beach. So I tried again a little farther into the ocean. This one was going to have a larger base with the water being deeper. I built the glass walls first and filled it with dirt. That was also time consuming but this is what I ended up with.

I think at this point I decided that this would be my main tower, with the other glass structure serving as an entryway of some sort. I'll get on that soon I guess.