Koh Phangan hosts many amazing places to enjoy your vacations.
Be sure to explore diving sites like the Southwest Pinnacle and Sail Rock which are half way in the middle. If you are more interested in snorkeling check out some of the beaches in Haad Salad and Haad Ya.
Do yourself a favour and rent a boat to explore the many beautiful beaches near Koh Phangan and even include in an overnight camping.
Koh Phangan has a very hippie vibe thats why there are many yoga centers and retreats on the island. Attend some yoga classes and detox programs in The Sanctuary. Also the Yoga Retreat is in Haad Salad is well recommended.