To me the most beautiful bookstore is one that is well organized. I don't particularly care what it looks like on the outside or where it is. When I visit a bookstore, I like it to be clean and orderly. Nothing more frustrating than trying to find a book in a store that is chaotic and cluttered. I've visited bookstores with tens of thousands of books piled up everywhere and no way of knowing what's in any pile. Sorry, but not worth my time to look.
There are certain writers I like to collect and whenever I'm near a book shop I like to stop by and see what they have. I often like to strike up conversations with the owners, most of whom run their stores as a labor of love (the internet has really cut into their business, but that's life). They're often quirky people but passionate about books, as I suppose am I.
I also like to visit Libraries during my travels. I actually find the quality of a library and extent of it's collection tells me a lot about the citizens and government of a city.
Books to me are sensual objects. I enjoy their touch and feel. I like the smell of the ink on the paper as I open them. Can't duplicate that with a Kindle (which I do own and use somewhat reluctantly). So visiting a nice bookstore anywhere is fun.