I just go a new passport. It's hard to believe it's already been ten years since my last one, which I got shortly before I moved to South Korea. Given the state of affairs in the world today, it's not an exaggeration to say that a fresh passport with a new ten-year life span means everything to me. And while the information available here for the US embassy in Seoul is mostly good, here are a few suggestions to make the whole process easier:
1) You will have to make an appointment through the embassy website (above). However, I was two hours early for mine (after taking the bullet train to Seoul from Daegu). I approached the officer behind the glass and he told me to come back in an hour. I came back and he let me in an hour before my "official" time. The point being, maybe I just got lucky but if you're early go ahead and get in line and maybe you'll get waved in.
2) Speaking of which, the map available through the website is a mess. The US embassy is located right next to the big statue of King Sejong in Gwanghwamun. The map suggests you go to something called the "American Center" but I'd suggest grabbing a cab and, logically, telling them to take you to the US embassy ("mi-guk-dae-sa-gwan"). My cabbie had no idea what "American Center" was, but US embassy? No problem.
3) The embassy itself is a surprisingly nondescript building, but with a bunch of South Korean police officers out front. Obviously, you can't go in through the main gate. But facing the gate, turn right, walk to the first intersection, then turn left. About half a block and to your left is the window that gets you in. This is where you'll want to have the print-out confirming your timed reservation. Like I said, I got lucky and was waved in early. Your mileage may vary.
4) They'll take your cellphone and ask you to turn it off. I left my beloved iPad back in Daegu, because they only allow one electronic device to be checked in. Could I have gotten lucky on this one as well? I have no idea. They didn't search my bag but I imagine they wouldn't be pleased if I'd tried to sneak it in.
5) Apparently they accept US bank or credit cards for payment (110 bucks, ouch) but I paid cash. In general, I always keep four or five hundred US dollars in my apartment at all times. I'm rather gangster like that. Bug-out cash, basically.
6) Be prepared to write your Korean address in Korean.
7) This is because they've adopted a delivery service, which is awesome in that you won't have to go back to Seoul. I was told the delivery would take two to three weeks.
8) In fact, having gone to the embassy on a Monday, I received my brand new passport on the Wednesday morning of the next week (nine days).
9) Strangely for Korea, you'll have to pay an extra 10,000 won to the delivery guy. I'm not sure what was going on there, but I was just relieved to be set for another decade of travel.
10) As for timing, the embassy suggests you do all of this six months before your current passport is set to expire. My expiration was coming June 2018, so I took care of all this in February. The process is mostly painless, so there's no reason not to renew as early as possible.
11) South Korean passport photos are a different size than American ones. The application sheet you fill out has a cut-out pattern that you can show to your photo studio person, and they should figure it out (two by two inches, which is 51 by 51 millimeters). There was a photo booth in the lobby of the passport services office but there's no reason to not get a professional job done in a country with photo studios on every block. A set of passport photos cost me 15,000 won.
And that's about it. The only hang-up when my number was called is that I had to take care of number six above. You hand over your old passport and all your paperwork, then they sort of package it all for you and send you to a cashier's window to pay. Done and done.
I'm willing to bet with a nine-day turnaround the processing took place entirely in country. Given the number of Americans in South Korea that's not too surprising.