I spent 4 days in Istanbul and I contracted 2 days with a guide, to visit the most important and interesting places. We were attended by Sinan, who speaks perfect Spanish and we spent 2 unforgettable days getting to know all about Istanbul, honestly without the explanations of a guide you cannot understand culture and museums. He tells you many stories, anecdotes and explains very well how the story was during those times. I definitely recommend hiring a guide and if you speak Spanish, Sinan is the best option.