Made some more progress in Rain World, if by progress you mean "mapped out more areas but still have very little clue how things work around here."
Made it to the area known as the 'Shaded Citadel' -- and, wow, does this place start getting dark when you go underground. And there are spiders. Fortuitously, I noticed they are afraid of bright lights, and was lucky enough to snatch a brightly glowing gem off a wandering creature (which I otherwise don't know whether to fear it). Made it very far across the area but, unfortunately, died about one screen away from the next checkpoint (and boy were there a lot of spiders scuttling about in the dark). I did, however, unlock an ability to fast travel so I warped back to the Outskirts and headed into a different area, which turns out to be the 'Drainage System'. I made it to one checkpoint (after unfortunately falling victim to one of those pole-mimicking plants, which was RIGHT next to the checkpoint room too), then continued exploring and found another (which, again, needed two attempts to actually reach). I keep forgetting about the pounce-jump maneuver. Oh, and I discovered that there are fish that apparently like to eat you, and it's also possible to drown (not that this should be a surprise in general). Now if I can figure out how to fast-travel out of here, perhaps...
But then again, fast travel IS a mechanic that sort of weakens the overall immersion, and game experiences generally feel more cohesive without it.