How do I get the Love Key?

[Jinti]

So I finally got fed up looking for the thing and looked up it's location, and it's behind an impassibly low ceiling hanging over a pit of acid. Dashing under and double-jumping don't seem to be enough to get me through. Is there something I'm missing here?

[Wanderer Yeumun]

Go grab the acid immunity from the Royal Waterway.

[Jinti]

Oh shoot, thanks!