When eight western lowland gorillas arrive at Congo Falls, an elaborate two-acre habitat that’s nearly complete at the San Antonio Zoo, they’ll have access to a seventy-foot climbing tower, the tallest of its kind anywhere in the world. Looking south through the struts at the top of Silverback Peak, the animals will be able to gaze toward the city’s iconic downtown skyline three miles away. They won’t, of course, recognize the Tower of the Americas, or the old Pearl Brewery, or the historic Emily Morgan Hotel. And they certainly won’t realize that the construction of their new home required digging out large amounts of limestone from the old quarry that underpins the zoo, nor that this mining project has—at least by some accounts—resolved a three-hundred-year-old mystery…