Castillo De San Marcos is located in old town St. Augustine. Construction began on the fort in 1672. Castillo De San Marcos lays claim to the title of oldest masonry fort in the U.S., and is one of only two forts in the world that is constructed of coquina, a semi-rare limestone.Parking and public transportation at Castillo De San MarcosCastillo De San Marcos is located on A1A in downtown St. Augustine. The uncovered parking lot in front of the Castillo is operated by the City of St. Augustine, and the charge is $1.50 per hour. The parking meters shut off at 5:00 p.m., so guests visiting after 5:00 will park free of charge. The Sunshine Bus makes stops at Castillo De San Marcos and fares are just $1.00 for one way trips.Best and worst time to go to Castillo De San MarcosWeekends from June through September are the busiest times, with crowds surging up to 3,500 guests daily. The park reports that the lowest attendance is from mid-September through November.Admission to Castillo De San MarcosAdult tickets are $7.00 and children under the age of 15 are admitted for free, but they must be accompanied by a paying adult. Tickets are valid for seven consecutive days after purchase. Must see/do at Castillo De San MarcosHistoric weapons demonstrations (cannon and musket firings) are held on Fridays, Saturdays, and Sundays - weather permitting.Other places to visit near Castillo De San MarcosA visit to St. Augustine would not be complete without seeing the St. Augustine Lighthouse and Museum. Insider tip for visitors to Castillo De San MarcosAccess a short climb to the top of the fort for picture perfect shots of Matanzas Bay. Be on the lookout for dolphins. Castillo is just a short walk to the Old City district, which is a prime spot for dining and shopping.Author's bio: Jamie Davis is a freelance writer and top-selling author with Llewellyn Worldwide. She lives on Wilmington Island, an area of Savannah, Georgia. She loves all things coastal travel, and if pressed to describe herself in one word, she would choose "traveler." She can be found at http://jamiedaviswrites.com.