This is one of the biggest mosques in Europe and has the most beautiful ornaments. As the name says the color that dominates in the arabesques is blue. It has a big yard where tourists usually spend most of their time, but when you get inside, it's a completely different experience.
Of course, before entering in the mosque, you will have to take off your shoes (that is a tradition). It's an Islamic rule that women can’t enter the mosques, but since this one is a popular touristy sight, women can go in, too. You can stay while the service is on, but the best time to look around is between 5 and 7pm because there is no service at that time and there are no believers, so you can just walk around and not be afraid that you’ll disturb somebody during their prayer. It’s a "must see" sight.
In the yard there is an old man who sells traditional Islamic hats -- they're very cheap and it's a beautiful souvenir that will remind you of this marvelous piece of art. Also there are many people that will tell you about the mosque’s history for a very cheap price-around five dollars. They speak many different languages, so you’ll understand no matter where you’re from.