I'm not sure what the parent is referring to. If you're an American citizen, you don't need a passport, just book a flight. Large numbers of the population speak English, and much of the US is already there. The roads are the same, the dollars are the same, hell, even the fast-food is the same.
Yes knowing what side of the road to drive on and understanding driving laws and being able to spend the currency you already have are indeed features.
Maybe not an adventure, but you can do some fun things.
- Culebra has amazing beaches
- Visit the bioluminescent bay
- Visit El Yunque. You can do the regular tour or visit other trails.
- You can go rapeling
- You can go SCUBA diving
- You can go visit reefs
- You can go zip-lining
They're not limited to PR, but you can do them someplace new/different.
You can escape the cold. (45° here and raining. I _kind_ of wish I was back in PR)
As a European not belonging to VWP you have to go through the process as if you were going to mainland US which is ridiculous. All neighbouring islands I can visit with visa on arrival - don't have to go to any embassy to beg for the privilege to visit your country.