I am writing this post in order to recommend you the courses that you can take while you are in Thailand. If you are a long-term traveler and want to learn something new here, this is my recommendation.
Thai Language: Thai language is similar to Lao language. If you are Western, you might think that Thai language is difficult (I think so!). If you are interested in the language and want to learn while you are here, just search in the internet for a language school. I am sure there are many Thai language schools especially in Bangkok. You can also hire a private tutor too, but it would be more expensive.
Thai Cooking: Thai food is one of the world famous foods. If you love Thai foods, you can take a cooking course or two while you are here. Just search for a course that teaches the dishes that you want.
Thai Boxing: Learning Thai boxing is now more and more popular for locals especially for women. You can easily find schools teaching Thai boxing from a basic course to professional course.
Thai Massage: Thai massage is well-known around the world. Many tourists have Thai massage at least once while they are here, and many of them want to learn Thai massage. The most famous school for Thai massage is at Wat Pho. Many Thais take courses there.
All courses are related to Thai, so taking them in Thailand is much cheaper than taking them at anywhere else in the world. Enjoy learning!