1) The word "book" contains two vowels: O and O.

2) The Grand Canyon, located in Arizona, United States, is a massive and awe-inspiring natural formation carved by the Colorado River. It is approximately 446 kilometers (277 miles) long, up to 29 kilometers (18 miles) wide, and reaches a depth of over 1.8 kilometers (1.1 miles).

3) The Olympic Games, originating in ancient Greece, were revived in 1896 and are now held every four years, bringing together athletes from around the world.

4) The largest living structure on Earth is the Great Barrier Reef, spanning over 2,300 kilometers (1,400 miles) along the coast of Australia.