Other important active volcanoes are Apo, in Mindanao; Catarman, on the island of Camiguin; Canlaon, sometimes also called Malaspina, on Negros; Caua, in northeastern Luzón; and Claro Babuyan, on the island of the same name. A considerable number of the volcanic peaks of the Philippines, including the one last named, have never been ascended. It goes without saying that in a country where there are so many active, dormant and extinct volcanoes hot and mineral springs are of common occurrence. On the slopes of Canlaon there are three of the former, known respectively as "the chicken killer," "the hog killer" and "the carabao killer," on account of the supposed destructive powers of their waters. The Tiwi Spring, near the base of Mayon Volcano, is famous. The water of Sibul Spring, in Bulacan Province, has medicinal properties of undoubted value, as do the waters of various other mineral springs, including those at Itogon and Daklán in Benguet. The scenic surroundings of some of them are most attractive, and doubtless important watering places will be established in their vicinity in the course of time. Gigantic limestone cliffs are among the most striking features of many of the more mountainous regions, and in some parts of the islands, especially along the coast of Palawan, rise directly out of the sea. They take on wonderfully beautiful, and sometimes very weird, forms and are often full of caves in which may be found the famous edible birds' nests, so highly prized by the Chinese. A range of limestone mountains ends at St. Paul's Bay on the west coast of Palawan. The bay takes its name from a majestic peak, with a wonderful limestone dome, which looks like a cathedral. Near it is another remarkable mountain called Liberty Cap, on account of its peculiar form. Beneath this range lies the scenic wonder of the Philippines, the famous Underground River, up which a ship's launch can run for more than three miles to what is called the "stone pile," caused by the falling of a great section of the roof. One may climb this obstruction, and utilizing native boats dragged over it by my party in August, 1912, may continue for a distance of half a mile, to a point where the roof of the cave drops to the level of the surface of the water, and further progress becomes impossible. A trip up this river is an experience never to be forgotten. There is no danger of getting lost, as the three short side passages which run off from the main cavern all end blindly. The channel has been mapped by the Coast and Geodetic Survey and is plainly marked at all critical points.