Caves?
Flood those tunnels?
A network of more than 220 subterranean caves stretches 286 acres below the bustle of the island’s heavily trafficked thoroughfares.
By Karina Martinez-Carter
14 November 2011
About an hour and half from the city of San Juan, far from the sandy, Caribbean beaches that lure most visitors to Puerto Rico, a network of more than 220 subterranean caves stretches 286 acres below the bustle of the island’s heavily trafficked thoroughfares.
http://www.bbc.com/travel/story/20111114-puerto-ricos-underground-caves