Wow. The Blue Mosque (or Sultan Ahmed Mosque) is incredible. Built in the early 1600's, this is a structure not to be missed if visiting Istanbul. I recommend reading more about this mosque on the Wikipedia page here.
This is really the one sight we went to see in the city.
I wasn't too keen on waiting in the loooooong line that wrapped around half the mosque... but Jaime new that the inside was supposed to be worth it. Thankfully, I think we had turned up right before it opened for the afternoon after the mid-day closure. The line moved rather quickly once the mosque opened up to visitors again.
It was free to go inside. We had to take our shoes off and wear disposable slippers. It was crowded inside - but mainly because of how incredible the inside is to see!!
I missed a good photo of the lights that were hanging. Thousands of lights were low throughout the mosque... and the domed ceiling was just stunning. WOW.