Sai Kaew Beach (Diamond Beach) is the longest and most popular beach on Koh Samet in Rayong Province. The beach faces northeast toward the Gulf of Thailand and gets full exposure to the northeast monsoon from November to March.

Due to the heavy tourist traffic, kitesurfing here requires caution. The beach is wide with a sandy bottom and clear water. Best suited for intermediate riders who can navigate around swimmers and boats. Early morning or weekday sessions are recommended to avoid crowds. The NE monsoon provides consistent onshore to side-onshore winds.