If your flying to Istanbul(Turkey) you need a visa. If your visiting by cruise ship you don't need a visa.
Last time I was in Istanbul overnight, a couple of months ago in fact, We had a troupe of costumed dancers and a belly dancer performing on the pool deck at night. This was one of the highlights of that cruise's entertainment as they were brilliant. If you see that the same kind of show is offered whilst there it's well worth staying on board to watch, Also the skyline views at night from the upper decks in Istanbul are worth a few feet of video. regards Neil.
No, when you arrive by cruise ship you do not need a visa.