Map of the Shara desert showing the major ergs (broad, flat area of desert covered with wind-swept sand with little or no vegetative cover) and mountain ranges. The red dashed line shows approximate limit of the Sahara. National borders are in grey.

The deepest place on Earth is in the Pacific Ocean. Within the Mariana Trench, the deepest place on Earth, there’s a small depression called the Challenger Deep, which reaches depths of 35,856 feet (10,971 m).

Starting from the early 17th century the Knights of Malta took care to surround the Maltese coast with watchtowers. By 1720, Malta's coast had no less than 24 watchtowers. Gozo had six, and another one was built on Comino island.