In the Land of Leadale 1x9

Cayna awakens with a hangover in a village out in the middle of nowhere. While she's dealing with a headache, she hears people talking about hearing singing coming from a well. In order to find out what's causing it, Cayna summons a flying fish and dives into the well. When she gets down there, she discovers a massive underground cavern. And what she finds down there is...