If anyone has any kids who might be interested in logic, I highly recommend his puzzle books. They might be fun for adults too, but I can’t be sure of that, as I haven’t looked at them for quite a few years—back then, though, I found them very accessible and they hooked me.
Satan, Cantor, and Infinity by Raymond Smullyan
Smullyan’s books are the best introductions to formal logic I know. They are witty, entertaining, and make you think—without it being work.
If anyone has any kids who might be interested in logic, I highly recommend his puzzle books. They might be fun for adults too, but I can’t be sure of that, as I haven’t looked at them for quite a few years—back then, though, I found them very accessible and they hooked me.