Sant Jordi, the 23 of April, is a special day in Catalunya. It's a romantic day similar to the American Valentine's day, but instead of sweet candies and chocolate, couples and friends give books and roses to each other. The street gets full (I mean, FULL) of people walking around with roses and the book stores open markets with discounted price.
If you're a single, don't be miserable on a romantic day by yourself. You can be as happy as couples if you find your favorite book in good price.