I just recently had a discussion about Visa, ESTA, ETA, etc. with my wife. After the London Do I am going on a cruise from Amsterdam to Norway, so I had checked if I need anything as German citizen. About the same time she was travelling to Georgia and on the way back staying 3 days in Istanbul. Reminded her to check for Visa requirements. She had done it for Georgia but not for Turkey, had assumed she could just travel there with a US passport.

She ended up having to pay twice for the electronic Visa because the first she did, she didn't save the PDF on her phone and had no service when getting to IST.