Tiny enhancements to existing structures

Instead of majorly revamping structures, add tiny little changes. For example, if the update isn't nether-focused but something entirely different, perhaps tiny changes to nether fortresses could be made. By that, I mean design changes (since the design's pretty old), maybe a new area or two. But no new blocks, nothing major. Just to spruce things up.

Specifically dungeons and mineshafts