"Rumors of tunnels under San Juan surfaced every year at one time or another...It was speculated that the tunnels had been used to move troops from one defensive position to another without being seen or exposed to enemy fire, which made sense. But others had suggested that the tunnels were also used by the Governor and his officials to travel unobserved to the garrisons, to other government stations, and even to the cathedral to hear mass." Justifiable Evil, Chapter VII, at p. 108.
The tunnels under Old San Juan actually exist. The National Park Service, in charge of the El Morro and San Cristobal forts, gives tours of some of the tunnels in the latter of the two fortifications. Some of the tunnels lead to blind alleys, and were designed to be packed with explosives, to be detonated under any unwary, advancing enemy that dared to invade the forts. A fleet-footed soldier would light up the fuse, and run out of the tunnel, hopefully before the charges went off. But other tunnels were used to move men unseen under the massive defenses and the city. A significant part of the story in Justifiable Evil happens in these tunnels.
"Czecka emerged from the small, low arched exit of the tunnel with the same startling implausibility of a clown climbing out of a tiny clown car. His shirt, drenched in sweat, clung to his broad back like a second skin. His nose, forehead, shaved pate, and arms were streaked with soot and dust." Justifiable Evil, Chapter XXVII, p. 304.
The photo above shows the actual entrance to one of the tunnels in Fort San Cristobal, which connects to other tunnels inside, and is very similar to the one described in the book. The portal is low and constricting, and the underground passageway into which it leads is foreboding and claustrophobic.
Many of the walls of the tunnels open to the public have been plastered, like in the photo above. But in their original state, "they were made of red...bricks, with arched ceilings that curved at a height of slightly more than five feet. The floor was nothing more than dirt hardened by the passage of feet and time, and in some areas water dripped from above, creating a muddy, slippery mire on which the device's wheels refused to roll." Justifiable Evil, Chapter XXVII, pages 304-05.
A perfect example of the prior description is the first photo in this blog. Also, see the two photos below.
Once you abandon the entrance and head into the bowels of the city, a suffocating darkness envelops you. The only way to see ahead or behind you is with an artificial source of light, and then, only a few feet are visible in either direction. "...The beam of his flashlight (bounced) over the curved walls and ceiling of the tunnel, encasing him in a bubble of light that opened up the impenetrable gloom ahead of him and rapidly closed behind him." Justifiable Evil, Epilogue, Chapter V, page 1118.
Sometimes, like in the preceding photo, the underground passage splits up, heading in two or more different directions: "The last stop occurred when the nine-person line had reached where the tunnel divided into two separate corridors like a giant "Y"....Both seemed to continue as far as the mini light beam could show." Justifiable Evil, Chapter LXIV, page 816.
Other times, the tunnels curve or make sharp turns. See, for example, the photo below.
"I think this tunnel was designed to help the Governor move under the city unobserved, and also as an escape route...The Spaniards were great at building fortifications and defenses. They hardly ever designed straight tunnels, where their enemies could rush straight at them or fire into them as they retreated. These passages were designed to disorient and confuse their enemies, and to protect their soldiers." Justifiable Evil, Chapter LVII, page 733.
Also, spread throughout many of the tunnels were small openings in the walls.
Above is an example of one of the smaller openings that appear randomly on the sides of the corridors, this one fitted with a modern lantern to illuminate the way. "The left tunnel initially extended for a long interval in an unwavering straight line, interrupted at irregular interludes by vertical niches in the walls, barely big enough to accommodate a man...Maybe ambush nooks for intruders who wandered inside, or places from where a rear guard could fire back on its pursuers...However, soon the tunnel angled slightly to the left, and began to slope downwards." Justifiable Evil, Chapter LXIV, page 818.
So where does reality end and the book's fiction begins? There is no doubt that there are tunnels under Old San Juan, probably under most of the city. However, the opening to the tunnel in the courtyard of La Fortaleza (the Governor's Mansion) described in the book is fiction, as is the tunnel leading to the El Abanico fort, and those passages beyond. That does not mean that they do not exist. But until their existence is verified, we will have to roam them through the corridors of our imagination.