Thought while typing: Will the problem of broken trans cavern-level passageways be fixed or at least minimized? They are at least common enough that you will eventually find one that does connect all the way through, but more often than not, they break somewhere, usually at the floor of the next cavern layer.
Is this bug report on the tracker?
I tried looking before and don't think I saw a bug report on that specifically, but I'll check.
Edit: Tried caverns as keyword, didn't find one, trying other keywords.
Edit2: Didn't see any reports about that issue specifically, but what I've noticed is that while the trans-cavern passages themselves are complete, they often have a spot (usually at the very top, but I've had it in other parts of the passageway) where there is an up ramp, but there is no corresponding downramp above it, just a floor blocking the way. It's not the same as, but is similar to
http://www.bay12games.com/dwarves/mantisbt/view.php?id=4520 . The passages are common enough that you will eventually find one that does go all the way through.
Given that he was working on the demon sites, dwarf sites and goblin sites (which are mostly underground), he might have fixed it along the way, no idea.