The Changing of the Guard at Deoksugung.

During the Joseon period, a government office called Sumunjang was in charge of the gates of the palace. Sumunjang, an official at Jong 6 Pum post, along with Chamha, Sumungun, etc. were responsible for inspecting and keeping public order during the opening and closing ceremonies of the City Gates. The ceremony consists of drum beating, setting a new password (each day!), checking the password to reveal each other's identity, handing over the palace key and confirming the truth of the order, and making a round of inspection to check the safety of the palace.

I was really lucky to be leaving Deoksugung in time to catch this!