A few suggestions you can look into:

•Mathematics: A Very Short Introduction, Timothy Gowers

• The Millennium Problems: The Seven Greatest Unsolved Mathematical Puzzles of Our Time

by Keith Devlin

•The Mathematical Century: The 30 Greatest Problems of the Last 100 Years, Piergiorgio

• The Calculus Gallery, William Dunham

• Letters to a Young Mathematician, Ian Stewart

• The Book of Numbers byJohn H. Conway

•Fermat’s Enigma: The Epic Quest to Solve the World’s Greatest Mathematical Problem, Simon Singh

•101 Careers in Mathematics, AndrewSterrett

•The Best Writing on Mathematics Series