You have two Spanish forts inside twenty minutes of each other. One of them will charge you fifteen dollars. The other one will not charge you anything, ever, including the boat.

Nobody tells you this. So here it is, off the National Park Service’s own fee pages.

The one that costs money

The Castillo de San Marcos is $15, and the fee is per person, not per car. Everyone 16 and up pays. Under 16 is free but has to be with an adult.

Two things about that fifteen dollars that almost nobody uses.

It is good for seven consecutive days. Not one visit. Seven days. Walk in Monday, walk back in Thursday on the same ticket. If you have people coming to town, buy it the day before they land.

They do not take cash. At all. The park’s own page says plan to go cashless, card only at the fee booth. Showing up with a twenty gets you nothing.

If you are going to end up there more than three times in a year, the park’s own annual pass is $45 and covers you plus three other adults each time you walk in. The America the Beautiful pass is $80 and covers every federal site in the country, which is the better buy if you are ever going to drive to a national park on purpose.

Hours: first admission 9 a.m., last admission 5 p.m., everybody out at 5:15. Open every day except Thanksgiving and Christmas. The grounds outside are closed midnight to 6 a.m., so the seawall at 3 a.m. is not a plan.

One more thing from the hours page, and it is the single most useful sentence on it: visitation is lowest from mid-September through mid-November. That is right now. A busy Saturday puts 3,500 people inside that fort. September does not.

The one that costs nothing

Fort Matanzas is fourteen miles south on A1A and the Park Service lists the cost of everything there at $0.00. Park, fort, ferry, all of it.

There is a catch and it is not money, it is timing.

You cannot get on the boat without a boarding pass. The pass is free, but you have to pick it up in person, that same day, at the Fort Matanzas Visitor Center. Not the city visitor center downtown. The park’s page puts that in capital letters, which tells you how often people get it wrong. Every human riding needs one, babies included. They do not hold passes over the phone and they do not issue them a day early.

They are frequently gone before 11 a.m. That is the Park Service’s own language: it is not unusual for all passes to be handed out before 11 on days the ferry runs.

No ferry Tuesdays or Wednesdays. Thursday through Monday, the boat leaves at 9:30, 10:30, 11:30, 12:30, 1:30, 2:30 and 3:30. Boarding starts 25 minutes past the hour and if you are not standing there, your seat goes to somebody else.

Budget 45 to 55 minutes for the round trip. Bring water, because no other food or drink is allowed on the boat or at the fort. Parking is small and the park says so plainly, so carpool. And if there is lightning anywhere near, the boat stops running until it moves off.

Park hours are 9 a.m. to 5:30 p.m., every day but Thanksgiving and Christmas. The phone is 904-471-0116.

Next Thursday, both of them are free

Sept. 17 is Constitution Day, and it is on the Park Service’s 2026 list of fee-free days. Every NPS site that charges an entrance fee drops it. That means the Castillo is $0 on Sept. 17.

It is a Thursday, which is also a day the Matanzas ferry runs.

The remaining fee-free dates this year are Oct. 27 for Theodore Roosevelt’s birthday and Nov. 11 for Veterans Day.

Cheapest version of this day: get to the Matanzas visitor center by 10, take the 10:30 boat, drive north, walk into the Castillo on a Constitution Day ticket that costs nothing. Two forts, four hundred years, zero dollars, and you are done by two in the afternoon.

If you are doing it any other day: Matanzas early, Castillo after, and remember the $15 is good for a week.