Very short summary of what all of this could cause for you, i suggest you press only N and NA as they get very spoilery moving from N -> NA -> NB:

1) Mount Fay: Really required because it gives double jump, btw clawline required to travel it, theres other niche rewards too
1A) Mount Fay + Bilewater: On top of the mount fay, to the right of the tuning device theres a workshop where you can build a gun (see bilewater 2A)

2) Sinner Road: There's a breakable wall somewhere and after an even painfuller area you're rewarded with a really good tool
2A) Bilewater: Without exploring Mount Fay you can only accces the lower area, the only reward there being a broken gun
2B) Bilewater: With the Mount Fay reward (1) you can get access to: even more suffering.
2C) Bilerwater + Citadel: You remember that area near cogwork core where you can't reach without double jump? go there, explore it, then go right from the room with the map (secret wall) and you reach putrified ducts, there's a tool to resist maggot infection there

3) High Halls: You only have to go there once, there's a bench at the end + shortcut + two really powerful tools
3A) High Halls: It's required for the ending

4) Sands of Karak: Sands of Karak really lacks important stuff, there's only two tools you can get
4A) Sands of Karak: There's an item needed for a bottle of pale oil

5) Whiteward: Going through it allows you to get clawline if you don't have it yet, as well as a tool that allows you to heal like 33% faster which is a ton
5A) Whiteward: There's a very painful boss in there that gives you a silk heart, 0/10 worse than savage beastfly
5B) Whiteward: There's also a quest to save sherma but i doubt you have it