Great ease of entry, plenty of things to look at. Diving is great, but snorkeling is a lot more relaxed, casual and easy to get people to go do with you! 

Island Tours, and fishing, diving, etc. If you're by the coast it's a great way to get around. For many islands, it's the only way! 

Get in the driver's seat and explore the area. It's as long as you want to paddle around, or rental time. Bring swimsuits, reef-friendly sunscreen and water. Even if you're not visiting a reef, it's nice to not kill all the wildlife around us! 

Very unique way to see the city situated in the hills. Go to the temples and hike one day, be free as a bird in the sky the next. 

Bring gear if you can, leave some of it if you want for the locals. It's kind of a respect/karma thing whether you believe in that or not. It's nice to do nice things. 

Grab some friends and hit some man-made waves. Wake surfing, kiteboarding, and wake boarding are all options. 

A little less high-octane than skydiving, but still an adventure! 

Located in Chiang Rai, expansive art collection and exhibition. 

There are a lot of elephant tours. Not all are interested in the animals' well-being.
Look for sanctuary and check that they are what they state. If animals are being posed, watch out they're probably drugged. And for free? Those lucky bastards.