Istanbul can be the whole holiday, and it is also a poor summary of a country that runs from the Aegean to the Iranian border. The city sits on two continents and works as a destination on its own: ferry, tram, steep streets, and a historic peninsula that is only one neighbourhood. Anatolia inland is another scale. The Aegean and Mediterranean coasts are a third pattern, with ruins and beach towns sharing the same water. Turkish is the language. English is common in hotels in Istanbul and the coastal resorts, then thinner.
Domestic flights are cheap and frequent relative to the size of the map. Buses are the old backbone. Between coastal towns a car is how you stop somewhere that is not a bus station. Istanbul has a metro, trams and ferries that are part of daily life, not a tourist extra. Cappadocia, the Turquoise Coast and the east do not belong on the same nine-day loop unless flying is the plan.
The currency is the lira. Cards work in cities; cash still matters in markets and small towns. If you need mobile data, the local rule for foreign eSIMs has been to buy before you land, because registration rules have made airport improvisation unreliable. Tea will be offered. Take it. A first visit that works is Istanbul, or Istanbul plus one inland or coastal region, not a sample of every famous name.
