Bear in mind that this area of Kwanghamun is a long way from the nearest subway. Yogwans will not have cooking facilities but little gas canister stoves are available very cheaply. Try to find somewhere with a communal washing machine as laundry services are extortionate. Do not expect air con. This is not Hong Kong or Singapore and Koreans are too tight to waste money on ventilation, so you will swelter wherever you are during the summer months.
Security can also be a problem.
Always have your own sturdy padlock and never leave the door unlocked while you sleep at night. Koreans know that teachers make good money and that we tend to avoid bank accounts. At one Yogwan I stayed at, locals held the Ajuma at knifepoint and forced her to unlock the doors of all the foreigner's rooms, so they could steal everything of any value. Nobody has any reason to go into your room, so do not give them the opportunity. The hangul characters for the word yogwan are probably the first that you will be able to recognise, partly because there are so many of them everywhere.