Southeast Asia forum

I will be traveling for the entire month of April. I have been researching and am starting to feel overwhelmed. Everything seems worthy of a visit! However I would like to stick to the your sage advice and not spend my vacation en route.

With that said I am looking for suggestions for MUST visit places in Southeast Asia. I have never been. I am interested in outdoor adventure (hiking, scenic places, amazing caves, etc), beaches (snorkeling!) and of course some culture (temples, street food, etc). I'm not looking to party since, well, I can do that at home. I also don't do well with museums nor a list of 1,000 temples (as I unfortunately loose interest after a few). I am on a pretty tight budget.

So oh wise ones, where do you suggest I visit? And please suggest how long I should consider staying in each locale and any other juicy tidbits that should be considered (i.e. transit).

Many thanks!