San Juan National Historic Site, located in Old San Juan, is the highlight of any visit to Puerto Rico. Go up and down circular stairs and ramps, enter secret tunnels, look out on the beautiful Atlantic Ocean and take a tour with enthusiastic, lively rangers.

Visiting Gates of the Arctic National Park is not easily done, but if you make the effort, the payoff is outstanding.

Here at the Traveler we recently asked you to comment on Which Is The Most Overlooked, Or Under Appreciated, Unit Of The National Park System? Well, after my trip to the U.S. Virgin Islands, I can answer with great conviction that the three intriguing parks in St. Croix -- Christiansted National Historic Site, Buck Island Reef National Monument, and Salt River Bay National Historical Park -- qualify for both overlooked and under-appreciated.

Ocmulgee National Monument, in Macon, Georgia, protects earth mounds from the Mississippian Period. The Earth Lodge Mound still has the original floor from more than a thousand years ago. The surrounding grounds offer a relaxing, easy, place to walk while you're exploring the monument.