This Puerto Rican tunnel is often called El Tunel Negro (The Black Tunnel), as its curved bearing permits for very little light to pass through. However, travelers who aren’t scared of the dark have a lot to look forward to - it opens onto a spectacular beach.

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The Guajataca Tunnel was constructed in the first years of the 20th century, as the American Railroad Company of Puerto Rico made a rapid push to expand transportation infrastructure. Puerto Rico had been annexed to the United States under the Treaty of Paris in 1898, and the Americans were eager for quick delivery of cheap sugarcane. However, in order for (tariff-free) exports to move at the desired pace, there would have to be a significant expansion of the national railway system.

The Guajataca Tunnel was part of a larger construction that would eventually connect San Juan in the north to Ponce in the south. At around 514 feet long, it is the larger of two tunnels (joined by a steel viaduct) connecting the towns of Isabela and Quebradillas through the Guajataca River Canyon. Trains carrying both passengers and sugarcane rumbled through it for nearly a century.

Although now only a paved walking path runs through El Tunel Negro, it remains significant as both a feat of engineering and a marker of a moment of political transition. It was declared a historical monument in 2000.