1) The word "mountain" contains three vowels: O, U, and A.

2) The Hubble Space Telescope, launched in 1990, has provided breathtaking images of distant galaxies and deep space.

3) The Great Wall of China is a UNESCO World Heritage site and one of the most iconic man-made structures in the world. It stretches over 21,196 kilometers (13,171 miles) and was constructed to protect the Chinese empire from invasions during ancient times.

4) The Age of Exploration, during the 15th and 16th centuries, saw European explorers such as Christopher Columbus and Vasco da Gama reach new lands and establish trade routes.