If you find that it's too far going to Seoul Mosque in Itaewon to perform your prayer, there's another good news! ^^
"The KTO recently opened a prayer room at the Tourism Information Centre on the first basement floor of its headquarters, so that Muslim tourists can visit. The carpeted room has a compass showing the direction of Mecca." by Joo Sung-hee, a KTO manager - sources: Halal Journal
The last time when I visited KTO HQ to make a free call to Malaysia.
How to go to KTO
Address : 40, Cheongyecheon-ro, Jung-gu, Seoul 100-180
Travel Information: +82-2-1330 (24hours)
How to get there :
1. Take subway line 1 and go out of Exit 5 of Jonggak Station. Go straight for 3 minutes. (The nearest)
2. Take subway line 2 and go out of Exit 2 of Euljiro 1-ga Station. Go straight for 5 minutes.
3. Take subway line 5 and go out of Exit 5 of Gwanghwamun Station. Go straight to Cheonggyecheon-ro for 6 minutes. KTO is on your right side at the Gwanggyo Intersection.