In he secret tunnels, Xanenetla Barrio, Puebla. 2 of 3. The tunnels are a system rediscovered in 2015. They are believed to be up to 500 years old and extend up to 10 Km. 477 metres of the tunnels are open to visitors. The tunnels were built after the foundation of the City in 1531. The tunnels begin in the historic center of Puebla and end at the Fort of Loreto and Guadalupe, where the Cinco de Mayo battle occurred. The tunnel open to the public extends for approximately four kilometres and has a height of over 8 meters. The tunnel connects the San Francisco River with the Guadalupe Fort, playing a strategic role during the French invasion in 1862.