My wife and I visited Seoul on the third leg of a 3 stop tour of Asia. We had some trouble getting there because we flew on a budget airline, and they were not really equipped for wheelchair travelers. In retrospect, I would not have flown on a budget airline, but with a more established carrier; at one point, I thought they were not going to let us on.
The Seoul airport itself is very nice and modern – make sure you get information here if you do not speak Korean, since most Koreans do not speak English. Pre-planning will be key to your trip because of the language issue. From the airport, it is an easy trip on the rail to get to the city center.
We made sure to print out copies of our apartment location in Korean (we stayed at an airbnb), along with a map and instructions for taxi drivers to get there. We decided to stick with using taxis because of the complexity of the subway – the Korean characters are hard to memorize or recognize. Also, taxis are reasonably priced in comparison to subways. We spent a lot of time looking for a reasonable and accessible airbnb. After asking a few different hosts to measure the doorways, we found one that could fit a manual wheelchair, and the pictures also looked like it would work. However, once we got to the apartment, the bathroom was smaller than expected, and we had some problems, which we eventually worked out. Not sure I would recommend it for others, so It may make more sense to stay at a hotel, especially if you are a power wheelchair user.
Like other places in Asia, there is typically a step or two to get into some restaurants, and if there’s a ramp it’s not up to US standards. You may have to ask an employee to help lift you into the main dining area. Alternatively, there are street markets with food and other goods readily available.
Museums and malls are a safe bet for being wheelchair accessible. We spent some time at the National and War museums of Korea, as well as shopping districts, like Gangnam. The national palaces are also worth going to, but are a little hard to get around with in a wheelchair due to the cobblestones.