80h-d

One thing I've noticed a lot of other than portals is that Jagex is making content above or below the ground level. One early example was the living rock caverns. Obviously it makes sense for that to be below ground, but still. They might have a modest building jammed into some small space on the map, but suddenly you go underground and there is a whole network. Consider the brass key into hill giants, or the yanille dungeon. Then there is the dominion tower and dungeoneering (again dungeoneering of course makes sense to be all below ground). That's just what comes to mind, there is tons of stuff that saves space by having upper and lower floors.