Pianta Sauna

From the Super Mario Wiki

The Pianta Sauna was a spa in Super Mario Sunshine. It appeared on the other side of Pianta Village near two massive palm trees. The spa closes at night, and releases many coins when sprayed and stomped. The entire sauna is a platform of white boards, with a bowl in the center. At the end of the area is the upper-half of a large Pianta statue. The game's developers had a sense of humor, as the water from the spa comes from the Pianta's nostrils.

Mario had to throw a huge Chain Chomp inside here, to cool it and its tantrum down.