Micromegas (Voltaire)
A great story from one of the greatest philosophers (18th Century); A Sirian and a Saturnian visit our planets (see 2 as yet undetected by humans moons around Mars) and visit the Earth where we look like atoms to them.
It's about how time and space are relative, how wars are futile and it's only 7 chapters.
Micromegas
Raoul