Me and my friends went to Koh Lipe, a small island of the Andaman Sea, in the Satun Province of southwest Thailand for a few days.
Around Koh Lipe there are several spots for you to see coral reefs. They are divided into 2 parts, the inner part and the outer part.
If you are on a tight schedule you can swing by 4 - 5 locations a day both inner and outer parts like what I did although, it's a bit tiring.
It's definitely a great experience overall with beautiful location and a great tour guide.