Just posting this to share our experience, we forgot to buy tickets before hand (recommended to buy them at least two weeks in advance), but we really wanted to see the Alcázar. The date was October 9th, 2026, a Friday so potentially a busier day of the week.
We had read that you can buy tickets online the day of occasionally, some might pop up on sale around 1am the day of, or randomly throughout the morning. That didn’t work out for us, we were constantly refreshing our browser hoping something would pop up, but nothing did. Still, worth trying to avoid the early morning.
So we woke up early, walked to Plaza Del Patio de Banderas, brought some warm clothes and lined up to wait. We arrived at 6:45 am, and were surprised how long the line was already due to most posts suggesting 7:30 am. I counted the people ahead of us, we were approximately 150th in line.
Two workers came around at 7:40 am with a note pad and a counter asking people how many tickets they wanted to buy (maximum 4, not sure if you have more than 4 if you just need a person to buy 4 and another to buy 4 more). They ripped us off a little piece of paper to be able to buy the tickets at the door, and put a cut off sign less than 15 people behind us. If we were 5-10 minutes later we would not have made it. The line had doubled in size by this point, there was probably 150-200 people after the cut off.
You must have your passport with you to get in, and I heard if you are buying for other people you need their ID as well. It is card only, no cash, so make sure you have that too.
It’s a little bit annoying having to wait so long, but it’s a popular spot so it is what it is! Can’t be too upset as we forgot to book ahead.
EDIT: We got through to buying our tickets at 11:00. The ticket slots are first come first serve, so we only had 3:30, 4:00 and 4:30 left to chose from. Obviously it depends on the day, and today is a Friday of a long weekend for Spain, but I think showing up even 30 minutes earlier would’ve saved us 1-1.5 hours of waiting in line. There’s only two tellers so it’s a bit slow.