I have an idea! Why not make a walkway at one end that goes under the water. It would be how you get to the center viewing area and you could put a couple of windows in it for added viewing while walking out to the center. Doesn't have to be very wide at all. I kind of have a similar design somewhere I'll have to dig up. Basically I want to do an underwater tank/pond also, but will need to buy the land first like you. Mine will be well down the road though. My idea was to do a 40' x 40' x 8' hole in the ground. It would be split kind of unevenly though. The walkway like I suggested would split it in half(sorta) On one side it would measure 40' x 20' x 8', then right next to that would be the walkway in the center. That would measure 40' x 10' x 8'. 10' wide for better viewing and photography. The viewing panes would be hella expensive, and I'm thinking I could just do the center with 4 panes of 8' x 4' x 3". On the other side of the walkway would be another tank for smaller species of fish. It would measure 20' x 10'x 8'. the 20' x 10' x 8' that's left would be the filter room. Completely underground. It would just have concrete poured walls with the windows inset for viewing. Above that I would make a partial green house with many solar cells to help with electrical costs, heating, ect. The big tank would be roughly 48,000 gals, and the other would be of course 1/4th that volume at 12,000 gals. Would be awesome, but we'll see if I'm ever able to do it or not!