the walls of the cave in which the longest navigable underground river in the world flows. puerto princesa, palawan, philippines

adventure asia background beautiful boat cave caves dark entrance excursion flows geological geology grot grotto heritage inside landmark landscape limestone longest mountain mysterious national nature navigable npuerto ocean palawan park philippines princesa puerto river rock sabang sail sea seven stalactite stalagmite subterranean tourism tourist travel tropical underground unesco unique walls water which wonders world