You will receive the frame for the Hot Spring once you log in to Treasure Isle and you can either place it on your island or store it for a later use. If you decide to place it, you will need to finish the building before being allowed to use it. Here are the requirements to complete the Hot Spring in Treasure Isle (different amounts for each of the 4 building stages):
– Rock
– Aqua Vitae
– Fire
– Glue
– Marble
After you manage to complete all the 4 building stages of the Hot Spring, you will receive a permanent boost of +3 energy to your bar. Well… that’s something it’s worth working to get!