There’s nothing like a total absence of safety measures to add a little excitement to a historical site. Within an hour of landing on La Isla de la Juventud, the Isle of Youth, I was clambering through an underground tunnel in the Presidio Modelo, or Model Prison, Cuba’s most dreaded pre-revolutionary prison, using my iPhone as a torch and trying not to slip on wooden planks and rubble. After squeezing up a rusty spiral staircase, I emerged atop a tower at the center of an enormous circular cell building that resembled a tropical Colosseum, where a single guard would once monitor more than 1,000 prisoners at a time.