The short version
Castillo San Felipe de Barajas is open every day, and the fortifications authority that runs it lists opening from 7am to 6pm. Tickets are sold at the gate and on the official site, which is also where the current rates live. We're not going to quote you a price here, because they revise them and a wrong number is worse than no number. Give the visit ninety minutes if you're moving, two hours if you go into the tunnels and stop for the view.
We send a lot of guests into the city for a morning before they come out to us, and this is the one piece of old Cartagena we'd put ahead of another hour of shopping in the Walled City.
What it actually is
It's a hill with a fort welded onto it. The castle was begun in 1639 on the Hill of San Lazaro, on the landward side of the city, and it was extended over the following century until it covered the whole slope. That's why it doesn't look like the neat square forts you've seen elsewhere. It's a stack of angled batteries, ramps and walls that grew by addition.
The famous part is underneath. There's a network of tunnels and galleries built to move troops and supplies out of sight, engineered so that sound carried, which meant defenders could hear anyone coming through them. Some are open to walk. They're narrow and low, and if you're claustrophobic you can skip them without missing the point of the place.
One more thing worth knowing before you climb: this fort held during the great siege of 1741, when a British fleet under Admiral Vernon tried to take Cartagena and failed. That's a large part of why the city still looks the way it looks. Standing on the top battery with that in your head beats reading the signage.
When to go
Go at opening or after 4pm. It's a stone hillside facing open sky and you climb the whole thing on ramps, so the middle of the day is work rather than pleasure. Early also means the top battery more or less to yourself.
If you want the history rather than the photographs, hire one of the guides at the entrance. The fort is not self-explanatory, and an hour with someone who can tell you which battery covered which approach turns a walk into something you'll remember.
How it fits into a day
The castle is a short taxi from the Walled City, so the obvious shape of a day is: castle first thing while it's cool, breakfast in the old town after, then the boat.
Our boat leaves the Muelle de la Bodeguita at 10am, 11.30am and 5pm, and the crossing to us takes 25 minutes. Take the 5pm and you can give the whole day to the city. Take the 11.30 and you'll want to be at the castle when it opens, which is the version we'd pick.
If you'd like a guide for the city as well, we run a Walking Tour of Cartagena for guests staying with us, either a Food and Culture route or an Art and Shopping one. You base yourself out here and go into the old city by day.
The forts nobody queues for
San Felipe defended the land approach. The forts that defended the sea approach are on our island, which is a thing most visitors never work out.
The San Fernando fortress sits at Bocachica, the village at the southern end of Tierra Bomba, guarding the mouth of the bay. We take guests over on a village tour: a five minute motorbike-taxi ride, then the rest on foot, ending with a beer with people who live there. It isn't restored to San Felipe's standard, and that's rather the appeal.
Up the hill from the village is the Angel San Rafael fort, which has the best view on our island. We walk up to it as part of a morning that finishes by cooking traditional Bocachica sweets with our foundation, which is a more useful hour than it sounds.
What to bring
Shoes with grip, because the ramps are smooth stone. Water. A hat. Cash or a card for the ticket booth, and a bit extra if you want a guide. That's the whole list.
And if you're coming out to us afterwards, book your boat seat before you go up the hill. There's no phone signal on our island but there's plenty on that one, and the boat fills.
See you on the boat.