This Spa is heavily inspired by Hotel Järvisydän (Lake Heart) in Finland.
It's probably the biggest single building I've done.

There are two saunas inside, three pools, a bar, dining area, aquarium, showers, dressing room, horse stable outside and a "love boat" in a small pond.

In addition, there is a small quest to be resolved in a small nearby village.

EDIT:
I never made it to Minecraft Marketplace so here's the download!
Remember this is for BEDROCK edition! I think there is a converter tool to make it work in java but you have to look for it yourself.