@Anneline *********
, You enter Thailand on visa-exempt scheme, not tourist visa, when you don't apply for Single/Multiple Entry Tourist Visa in advance to your travel. You will be stamped for 30 days without visa or pay a fee at the entry point. It is still eligible for 30 days tourism extension as Tod mentioned. You can to border bounce (go and back to neighbouring country) at the end of your stamp to enter on visa-exempt again. Or you can go to the Thai embassy in one of neighbouring country to apply for a Single Entry Tourist Visa. All up to your decision.