Purely theoretically, I was struck by the idea of making a bridge between Iron and one of the islands towards Snow as a means of uplift and wanted to play around with a few numbers. It quickly became clear that making pylons from the sea floor with MEW would be chakra prohibitive(over 100 times more expensive than the method outlined below) so I focused on using the 5 seal barrier. Assuming that we use 6m by 0.3m by 0.3m MEW chunks attached together, each with its own 5SB, a mile of bridge comes to 1340 seals and 300 chakra points(MEW makes 2.85 cubic meters of granite for 6cp). If a seal takes 5 minutes to make, that's about 14 eight hour days worth. There are some ways to cheat this, like only using 5SB on every other piece or if Akane makes us a polygraph, but I digress.
Obvious problems with this idea: attracts a lot of attention, exposes our seal work, what do we gain? A possible improvement would be to use a suspension design, since it seems highly abusable with 5SB, but I'm not a civil engineer and neither is anyone in the party, unless Kagome has been holding out on us. Specialty for Akane, anyone? I mostly did this because I'm interested in Snow. We know almost nothing about it and it seems like one of the few areas where scorch squads would have a hard time picking off stragglers innocuously.
Something that came up that's related to figuring out what happened with Uzu: can we safely search the ocean floor? Assuming it's at least a mile deep, henges probably won't be strong enough to hold up to the pressure. A light source shouldn't be a problem. Maybe the pangolins have figured out submarines? Do we know about the bends? Is this problem trivial using 5SB, water tight design, and oxygen supply? If I understand 5SB correctly, a structure containing all 5 seal internally(and therefore invulnerable from outside) isn't disallowed as long as the seals are the requisite distance apart and the larger structure is entirely one object. If the support seals aren't allowed to be on the same object as the barrier seal, then they can be on rocks contained in the box, or submarine, or what have you instead.