Starting from the Sinchon subway near Yonsei University. I would suggest taking Exit 3. Walk straight towards Yonsei University.
You'll pass a lot of stores and people along the way, then arrive at the front gate.
Walk in, on your right you'll see a map of the campus.
Look closely at the map, you'll see the route that you can take to arrive easily. The route I took kept me walking on the right side until I arrived at the building. That meant passing buildings 83, 82,78,77,40,41,58,59, to arrive at 61.
Then you can arrive at room 112. I didn't take a photo inside because there was a class going on at the time.
FYI, here is the sign in very clear Korean that you can show to people in case you somehow get lost.
CJL
"When you come to a fork in the road, take it."
--Yogi Berra
Here's the map's name in English. You want to arrive at building 61.
In Korean
From the map, you need to walk straight into the campus.
Here's the first challenge. A fork in the road. At this fork in the road, walk to the right.
You'll walk up the hill, see signs like this letting you know you are going in the right direction.
Walking up the hill you'll arrive at another fork in the road. Continue walking on your right.
You'll know you are close because you'll pass the President's Residence.
You'll come to another fork in the road, with a security box in the middle. This time, walk to the left.
There is, by the way, a bus timetable. If you can understand it, then you can try to use that.
That's what New Millennium Hall looks like on one side.
If you miss the turn, here's how it looks from the other side.
First floor, walk in, you'll see this small sign.
Then you can arrive at room 112. I didn't take a photo inside because there was a class going on at the time.
FYI, here is the sign in very clear Korean that you can show to people in case you somehow get lost.
CJL
"When you come to a fork in the road, take it."
--Yogi Berra