The Seas of the Moon
The moon's near side -- the side that's almost always visible to the earth. Visible features of the near side on a full moon are the its craters and "seas" -- the dark areas. Previously(before the high end telescopes and moon explorations), the dark spots of the moon were thought to be bodies of water -- seas -- by the astronomers observing using their telescopes. Some of the features were later named as seas, hence, "sea of tranquility", "sea of serenity", etc. They would later turn out to be large valleys and lowlands. The lighter and higher areas, brilliantly illuminated by the sun and has a slightly different surface are called the "highlands" or terrae.
The Apollo 11 moon landings(first time a man landed on the moon by traversing more than 380,000 kilometers) were on the area called the Sea of Tranquility.
Shot taken from Badian, Cebu, Philippines