Istanbul is the most popular city in Turkey.
James Bond first travels to Istanbul in From Russia with Love where he teams up with head of Station T, Kerim Bey to retrieve a Soviet cipher machine from Corporal Tatiana Romanova. After Felix Leiter's wedding in Licence to Kill, Bond is told by M that he was supposed to be in Istanbul on an assignment rather than pursuing Franz Sanchez in Florida.
He later revisits in The World Is Not Enough when Elektra King holds James Bond and Christmas Jones at the Maiden's Tower before he was rescued by Valentin Zukovsky. Bond then stops Renard from causing a nuclear meltdown in the reactor of a Russian submarine. In Skyfall, Bond and Moneypenny pursue Patrice through the Grand Bazaar, who is in possession of a stolen hard drive with intel on undercover NATO agents.