Khon theater is a traditional form of drama in Thailand based on epic story Ramakien.
The performance is made only by male actors dressed in very colourfull costumes
If you are looking for something interesting in Thailand Khon theater is the thing that you should see. There are many free performances in Bangkok, but the hardest thing is to find one for free. I am lucker, because I seen two performances and on one of them I was able to go backstage.
http://www.salachalermkrung.com/event.php