If you are a US citizen, you do not need a passport to visit Puerto Rico. If you are not a US citizen, I've always assumed that the same rules applied as if you were visiting any other part of the US. Am I wrong?

Myrtle Beach can be crowded. There are thousands of hotel rooms there and it is a major summer vacation destination. I've gone in September when it's much quieter and enjoyed it. I like it less in July/August but the beach there is wonderful no matter how many others I have to share it with.