I'd also recommend Sophie's World as a jumping off point into multiple "canon" works as referend by another poster.
I'm sure people out there criticize it as not rigorous or full of inaccuracies, but I've found it an easy read that gives a good overview into the works of western philosophy.
I’ve seen many syllabi that include this book. I haven’t read it myself but have met some smart/thoughtful students of philosophy who did and value it highly.
Just make sure you get the correct book. I put in a request with my library and accidentally got this:
https://www.amazon.com/Sophies-World-Sophie-Book-1/dp/031070...
I'm sure it's charming, but not what I was after. You want the one by Jostein Gaarder.
For an introductory overview, you could do much worse that Sophie's world.
This is actually what I came here to say! It is great book that I have given to many people. I also recommend Anathem, by Neal Stephenson which is a romp of a novel shot through with philosophy.
Got this as a gift from my teacher at the end of my last year in primary school, still one of the greatest gifts I've ever received
It was written by a teacher and geared at young adults. So its not a rigorous introduction. But its a short read and by the end you'll have enough leads to follow.
[0] https://en.wikipedia.org/wiki/Sophie%27s_World