Carlsbad Caverns were a unique set of caves on Earth in New Mexico.
While T'Pol was stationed in Sausalito, she took a five-day leave, visiting Carlsbad Caverns, along with Yellowstone National Park and Carbon Creek, Pennsylvania due to "scientific interest."
Later, in 2152, after telling a story about her second-foremother T'Mir, T'Pol listed Carlsbad Caverns among the places she visited while on leave on Earth. (ENT: "Carbon Creek")