In order to unlock the challenge floor of the Spire of Courage, you need to meet Hellhound, fight her in the advanced dungeon floor, and then check the Aldlyn city board to get an invitation to the challenge floor.
The dungeon in Siriveta has water fairies since two updates ago, so you can get the water bottles there as well.
The npc to start Ryoko's event is in the bottom right corner of the stronghold map.