OS X Yosemite: iBooks, Where are my books stored

Now with the new iBook application on OSX (I'm using Yosemite). The books are a bit harder to find.
I wish it could be as easy as finding song in iTunes. But it's not.

You just have to go look here:

It's by users, and it's amazing all the stuff you can find there...

Using terminal you can got into epub files and look at it's content.

Happy learning.