Koh Phangan
Nicknamed Samui's little sister, Koh Phangan is famous for its beach parties : especially the iconic Full moon.
Easily accessible by ferries from Samui :
https://www.seatranferry.com
https://www.lomprayah.com/
Ang tong national park is a haven for lovers of pristine nature, located 1 hour by speedboat from Koh Samui, made up of 42 islands in the Gulf of Thailand.
Koh Taen and Koh Madsum are small islands that often come together as a package, a short boat ride from Samui's south coast.