Go Up the Galata Tower at Sunset
One of the best sunset spots in the city is up at the top of Galata Tower, a medieval stone tower that dominates the city since the 14th Century and it offers an unbeatable panoramic vista of Istanbul's historic peninsula. The tower is nine storeys tall and you can see all the major tourist attractions like Hagia Sofia and the Blue Mosque all the way from here. Once inside, you can take one of the 2 operating elevators to get to the top level where you will find a restaurant and a cafe if you wish to rest, or you can just walk out into the balcony and be blown away by the view of Istanbul cityscape.
The cityscape is especially beautiful during the sunset and the blue hour right when the city lights up and before the sky turns completely dark. Depending on the season, you are going to have time for the sunset carefully and spare some time to go line up and go through the crowds to get to the top. The entrance fee for the Galata Tower is 100 TRY per person. The tower opens from 8:30 AM to midnight in the summer and 10 AM to 8 PM in winter every day of the week.