First, the disclaimer that is also the most useful sentence on this page: visa rules are set by governments, change without consulting tour guides, and depend on your exact nationality — so treat everything below as orientation, and verify your case at the official sources linked at the end. Now, the orientation.
The broad picture
Türkiye keeps entry deliberately easy for tourism. Citizens of many countries — including most of the EU, the UK, and much of Latin America and Asia — enter visa-free for stays typically of 30 to 90 days. Many others (historically including the US, Canada, Australia and China, though rules shift) use the e-Visa: an online form at evisa.gov.tr, a card payment, and an emailed authorisation, usually within minutes. No embassy queues, no paper in the passport beyond a stamp.
The e-Visa warning every guide repeats: use only the official evisa.gov.tr site. A cottage industry of lookalike websites sells the same visa with heavy markups and occasional fiction. If the URL does not end in gov.tr, close the tab.
Passports and cruise guests
Passport validity: Türkiye requires validity beyond your stay — six months at entry is the traveller’s safe rule, and some carriers enforce it at check-in regardless. Cruise passengers enjoy a long-standing courtesy: day visitors arriving by cruise ship for shore excursions are generally admitted without individual visas under group arrangements handled by the ship’s agents — one reason a Kuşadası port day is so frictionless. Overnighting ashore or joining/leaving a cruise in Türkiye changes the picture to normal entry rules.
