The Devil's Sentry Box is a small stone watch-post jutting out on a spur of San Cristóbal's outer walls, isolated from the main fort by a narrow walkway. According to one of the city's enduring legends, a Spanish soldier stationed here one night simply disappeared — uniform, rifle and all — and was never seen again. The likeliest explanation is that he deserted to be with a local woman in La Perla below, but Spanish military reports for the next two centuries kept the disappearance as "El Diablo took him."
You reach the garita on a short path from the lower terraces of Castillo San Cristóbal. The sea is loud underneath, the wall is narrow, and on a windy day it is genuinely unnerving — which is the point.