Reigen struggles a bit to swim back to the shell structure in the wake of the rumbling rough water, but then he sees the secret passageway. "Aha! Well, if this is manmade and was activated by the troubled water here, maybe it's a path to an underground shelter...or a secret path to the castle?" Wandering in the dark underground seems like it'd be dangerous, especially underwater, but this is either a valuable lead or a path to a secret treasure. Both could be worth it.

"Were there any flashlights with the equipment? You'd think one of these suits would have headlights or something."