I found 100억 (Baek-oak) with my Korean tutor. It is located in Gangnam on café hill. It is quite large, decorated very elegantly and is very quiet.
My Korean tutor and I met in Gangnam often because it was the most convenient location for both of us...it was halfway between each of our houses. We tried to go to some of the cafes we usually meet at (ie. Standard Coffee Bar, Angel-in-Us, Espresso Public), but all of them were full and very loud. We decided to keep venturing up café hill until we found a quiet place for our lesson.
The cafe's exterior is very grand. It is two-stories tall and is a very beautiful building with sweeping/curved lines and there is a beautiful garden in the front. The garden has a few strange/eccentric decorations, however. For example, there is a huge American football player statue out front. I don't know, I will never know.
The café is very elegantly decorated. The chairs are upholstered and there are a ton of other very European decorations. There are couches that remind me of living rooms in old people's houses. The color scheme is also very...geriatric. I don't really know how to describe it.
Additionally, there is a safe in one of the rooms with a bunch of 10,000KRW notes in it. Oh, I should explain the name of the café. The number 억 in Korean means one hundred million. So, the cafe's name is 10 billion. The safe probably is supposed to represent 10 billion Korean won. So kooky. They also have a wall devoted to autographs of famous customers.
Anyway, since this café is in the café hill area of Gangnam and they have this "premium look", the prices are a little expensive. Hot teas are around 7,000KRW, espresso-based drinks are around 8,000KRW, smoothies are 9,000.
My green tea bingsu (녹차빙수) was 9500KRW. It was pretty good, but not the best bingsoo I have ever had. The shaved ice is topped with a scoop of green tea ice cream, bananas, and fudge sauce. There was not very much condensed milk in it, if at all, so the flavor was only so-so.
On top of the strange décor, the café also hosts "gag concert" nights. I don't really know what to make of this place.
It is also known as a good sogaeting (Korean blind date) location, so I'm sure there would be a lot of interesting observation to be made later in the day.
I would probably never go to this café again. It was far too strange and expensive and the food was only so-so. I'm sure there are plenty of other places around that are better.
Gangnam Station exit 11. Walk straight until you get to the CGV and then turn right. Walk up the hill, pretty much to the top. You should see 100억 Café on your right.