There are a limited number of natural wonders to discover on each map, determined by the map's size. They are created and placed automatically at the beginning of the game. Natural wonders are impassable, and cannot be improved in any way. Some of them also provide an additional boost when inside a territory. Natural wonders provide a permanent boost to your empire-wide Happiness when discovered. Most of their bonuses apply only if they are worked by a city, and they only apply to that particular city some bonuses, however, apply empire-wide, or to any unit that comes close to them (even if it doesn't belong to the civilization that controls the wonder).
These benefits take the form of various production capabilities, including Culture, Science and Faith, which aren't normally available on land tiles. They inspire awe in any civilization that finds them and provide various benefits to whoever controls them (that is, includes them in his or her empire's territory and works their tiles). Natural wonders are unique terrain features, masterpieces of Mother Nature, which possess exceptional qualities that make them very different from the average terrain.
