It's clearly yet another one of those "wizards' lairs" -- one of the many that seem to dot the less-frequented alleyways and back streets of Seoul -- but one with a knowing difference; that dark doorway at the bottom of the stairs, appropriately spooky and sinister, looks to be the obvious means of gaining access to the mysterious realms beyond; however, its very obviousness makes me suspect it's actually a ruse, a false lead designed to distract the curious away from the real entrance -- that oddly chopped off-looking "tunnel" above it.
Now for the left turn: for the life of me I could not recall the snappier, harder-hitting term for 'false lead' that I knew existed. I wracked my brains all last night, trying to remember, to no avail. Then this morning I just happened to take down my copy of Charles Fort: Prophet of the Unexplained by Damon Knight, opened it at random, and there it was -- "...red herring".