America, North America, Park, U.S., US, USA, United States, United States of America, Yellowstone Park, alone, bacteria, ecology, ecosystem, energy, energy source, environmentalism, extremophile, human, human being, human beings, humans, land, lonely, masculine, men, natural resources, outdoor recreation, person, recreation, reflection, reflective, scenery, skies, solitude, sports & recreation, sun rays, sunlight, suns rays, thermophile, walk, walking
