>>2216377>layering and bonding acrylic or polycarbonate sheets could in principle work for making quite large windows in a submersive structure. Might not even be necessary. For Nemo's Garden, the grow domes weren't very strong/rigid at all. This was possible because they were at ambient pressure. The air was pushing just as hard against the inside of the dome as the water was against the outside, equalizing forces and holding the dome stable. If you wanted to seal a container so it remained at surface pressure, you would need strong acrylic because the water would be pushing much harder than the air inside, so you'd need to hold that pressure out.