|“||Located deep in the forest by Elendia, it is always filled with fresh water.||”|
This is a sublocation in Elendia's village divided into two "rooms", the spring entrance and the spring itself. Outside the spring is a small lot of sand, which has no real significance in the game. Nono is also found here, and if you rescued her in Heaven's Gate, she'll give you the Ribbon. Within the springs, you will find a rather mean fairy named Lulu, and an Undine name Meute. Meute is the only known Undine inhabitant of the spring, despite it being called Undine Spring.
There are a total of two reward bath scenes that occur within Undine Spring. The first one involving Lina and Fia occurs after the Nelde Ruins stage. To trigger it, make Lina and Fia collect the Paradise Plume, which is at the apex of Nelde. The girls will fall down into some pit filled with mud and they will become dirty, and will agree to take a bath as soon as they get back home. Next, go straight to Fia and Lina's Place and speak to Coco, and she will accidentally spill the beans about what they are doing. Afterwards, leave the house, and Ein and Rose will have a brief conversation, concluding that the girls may have gone to a spring. Go straight to Undine Spring and enter the spring to get the scene. If you go anywhere else first and then head to the spring later, you will be too late, as Ein will catch the two girls leaving instead. The PSP port added a minigame as a last resort to slink the bath scene from your grasp, so be quick.
The second one involves Cierra and Serene and takes place after the Tetyth stage. You need to have collected the Mint in this stage, which is located on the Aura Plateaus; the Mint requires a Trigger Point. Like before, go to Fia and Lina's place and talk to them. Lina will absent-mindedly tell Ein that Cierra and Serene are bathing, and Fia will quickly try to refute that and cover up under the guise that they're "washing clothes" (an obvious lie). Head to the Spring once again and take out the Golem guarding the entrance. This is not a battle, but rather one of those little mini games requiring you to mash a button repeatedly before time runs out; in the PSP version, there's a second one that requires jitter-clicking to complete successfully.If you manage to get past the obstacle(s), you're rewarded with the second and last bath scene.
The Fanelia weapon can be found in the sand at the entrance of Undine Spring after stage 5 and 6. You must look/quest the sand 5 times to find it. The Fanelia is the most powerful weapon in the game dealing 999 fixed damage for 8 consecutive hits. This totals to a whopping 7992 HP worth of damage (assuming all attacks hit). This mighty skill can only be used by Ein releasing it as 'Fanelia Beam'.