go to the embassy - the visa is 45 dollars. If you use the visa service it is 86 dollars or so. I will be leaving the Noordam (Rome to Istanbul sept 16th) as you are boarding -
I have been to Istanbul previously - it is a wonderful city!
Must see the Hagia sophia, Topkapi Palace, the Blue Mosque. If you have difficulty walking, take a tour. There is a good bit of walking once inside these sites - thought you might want to know!
Enjoy the trip!