From: http://www.facebook.com/event.php?eid=122337691138566

This is the meeting point, at the location of the marker: http://tinyurl.com/342b9wr

If you can get your bike onto a train, there are three nearby stations:
경 복궁 / Gyeongbokgung on line 3
광화문 / Gwanghwamun on line 5
종각 / Jonggak on line 1

View of the entrance to the area where the ride meets up:
http://tinyurl.com/34jfkqy

The ride starts at 4pm (or a bit later) and ends an hour or two later at the riverside in Youido.

Please post any questions and I'll try to answer.