Fort San Lorenzo stands on a cliff above the mouth of the Chagres River, and from the old walls you can see the Caribbean on one side and a green tangle of jungle on the other. It was built by the Spanish in the sixteenth century to guard the point where the river meets the sea, because the Chagres was the water road for the treasure caravans coming across the isthmus. A fort was only as good as its garrison, though, and in 1671 the Welsh buccaneer Henry Morgan took it, with a force of a few hundred men, before marching on Panama City itself.
The ruins have been battered by earthquakes, storms and a lot of vegetation, but the thick stone walls, dry moat and cannon pointing out to sea are well preserved. UNESCO lists the fort together with Portobelo as one of the key military works of Spanish colonial America. The view from the ramparts over the river mouth is the real treat, and in the early morning toucans and parrots make a racket in the trees. Howler monkeys sometimes join in.
Getting there is half the pleasure. The road passes through the old Canal Zone, former American territory, where rows of tidy military buildings from the early twentieth century still stand under big shade trees, now mostly abandoned. It runs past the Gatún Locks, where ships are lifted up into the canal, and then through dense second-growth forest on a narrow road with potholes and sudden puddles. Rain is very likely in the afternoon, and the heat can be fierce. The road is quiet, but watch for large trucks and for animals crossing.
Services are limited near the fort, though there is a small visitor centre. Colón, about twelve kilometres away, is the nearest large city, with fuel stations, supermarkets and workshops, and Cristóbal is closer. Be careful in the city itself, where some districts are rough, and do not leave the bike loaded and unattended. Fill up before you head into the forest, and bring plenty of water.
The dry season, from about January to April, is the best time to go, with clear light and fewer mosquitoes. Early morning is better still.