Complex sentence: The long coast of the Gulf of Thailand has many sandy beaches, the most famous one being at Hua Hin, which has been a popular resort since King Prajadhipok (Rama VII) built a summer palace there.
Split into simpler sentences: The long coast of the Gulf of Thailand has many sandy beaches. One of the best known, Hua Hin, has been a popular resort since King Prajadhipok (Rama VII) built a summer palace there.