1) The Nile River, spanning approximately 6,650 kilometers (4,130 miles), is the longest river in the world. It flows through eleven countries in northeastern Africa, supporting various civilizations throughout history and serving as a vital source of water and transportation.

2) The highest-grossing concert tour of all time is U2's "360° Tour," which earned over $735 million in ticket sales.

3) The concept of federalism involves the division of powers between a central government and regional or local governments, allowing for shared governance and autonomy for different levels of administration.

4) J.K. Rowling's "Harry Potter" series of books has sold over 500 million copies worldwide and has been translated into 80 languages.