Unfortunately for Galois theory there isn't anything suitable for high school students, but the nice introduction is here Galois theory for beginners, John Stillwell, in addition to historic essay in the introduction to the book by Edwards.

for arithmetics, I think the books by Alan Baker (Theory of numbers) and by G.H. Hardy might be helpful.

for geometry/topology this essay by S.S. Chern can provide some motivation for the subject.