What's a book that just makes you happy...?

I’m mostly looking for non-fiction. For instance, whatever device I have, there is a good chance I have the Dalai Lama’s ‘Art of Happiness”.
With the advent of ebooks, it’s so handy to have a book always with you, but I digress.
So, recommendations? It could be anything; I won’t shoot down one’s choice, as this is very subjective. In fact, I’ll put it in social, so maybe we can expound a bit, and perhaps share why it makes you happy. Looking forward to the suggestions!