Istanbul

The richest sightseeing on this list, with the longest trip in. Istanbul Airport sits far north of the old city: the M11 metro reaches Gayrettepe, but getting on to Sultanahmet by metro and tram can take more than an hour each way, and road traffic is no faster at busy times. Budget at least nine hours if you go alone. Turkish Airlines passengers connecting between two international flights on one booking can join Touristanbul, its free guided tour for layovers of 6 to 24 hours, which takes the transport worry away. Either way, Hagia Sophia, the Blue Mosque and the Basilica Cistern sit within a short walk of each other, so one neighborhood fills the day.