1) The word "piano" contains three vowels: I, A, and O.

2) The concept of gravity was famously described by Sir Isaac Newton after an apple fell on his head.

3) The Eiffel Tower can be 15 cm taller during the summer due to thermal expansion.

4) The Mongol Empire, under the leadership of Genghis Khan, became the largest contiguous empire in history, spanning from Asia to Europe.