Ah, the classic adventure duo dynamic! 'Log Pose and Wado Ichimonji' over on Archive of Our Own is the one I keep going back to. It's a long, episodic thing where they get accidentally stranded together pre-timeskip and have to navigate some weird, uncharted Grand Line island. The author nails their bickering-but-professional dynamic—Zoro's terrible sense of direction is a plot point, not just a gag, and Nami's navigation skills actually save their hides in creative ways. It feels like a lost arc of the manga, complete with original mythologies and weird sea creatures.
What I appreciate is that the adventure isn't just a backdrop for romance; the tension builds naturally from them relying on each other in survival situations. The pacing is methodical, sometimes a bit slow, but it makes the world feel vast and unexplored. The last update I read had them deciphering ancient poneglyph-like markings in a cave, which was a cool touch.