The Eternal Youth Spa was a spa owned and run by Poison Ivy.
The facility was built on the outskirts of Gotham City so Poison Ivy could exact her revenge on the wealthy businesspeople whose companies had exploited the Earth's resources. Poison Ivy sent videotaped invitations to various wealthy people, posing as Dr. Daphne Demeter, and offered them a free treatment at the spa—boasting a new method called Demetrite treatment. The spa was equipped with a variety of recreational facilities and an extensive lab facility where Ivy performed her research. When Batman discovered Poison Ivy's plan of turning people into trees, he went to the spa and defeated her. In the fight, several containers of the super-concentrated transformation formula were broken and fell to the ground. As a result, a massive tree grew out of the soil and completely destroyed the facility.