Enigmatic Entrance (Patreon)

Request made by a Patreon member!

A sequel to the previous request:

https://www.patreon.com/posts/76267640

After helping her free herself from the rock, Nami and Bruno are swimming deeper towards the cave, and they ended up finding what seems to be an entrance to a place, a castle? Fortress?

But before they can enter, they must deal with a riddle in front of them, as a time above them shows how long they've been there.

While the puzzle itself doesn't seem like a problem for them, they must make sure they don't drown after staying submerged for that long already.