I know this forum is full of category suggestions, but hear me out:

With the release of OSRS on Steam as of today there are measurable in-game achievements, all of which are free-to-play. Most games with achievements have categories for completing them all, and it seems reasonable to assume OSRS should have one as well. I think the achievements lend themselves to both being interesting to plan a route for, and also relatively straightforward to complete in a single sitting.