Not far from where I live, but inaccessible by metro, is an area called Yeonhui-dong. Many who live in Seoul haven't even frequented the area. It's really low key, and there are a bunch of hidden gems like cute cafés and boutiques. PS. I particularly like Manufact Coffee for a cup of that strong-strong.
A friend of a friend, Minkyeong Jin, actually owns my favourite boutique in the area, called Soft Selectshop. Though, she did mention, she will move the shop to Hannam-dong really soon. Soft carries lots of unique feminine statement pieces, and lovely items for the home as well. The shop is well known for it's iconic 'Soft Baby' unicorn candles, which Minkyeong designed herself, and makes with her husband. She has also started designing purses, as well as collaborating with other Seoul-based brands (like Diagonal and Nu Issue). You can catch the full article I wrote for Seoul Magazine here: http://bit.ly/2cBkVJI
SOFT online shop: www.softseoul.com
Shop Instagram: @soft_selectshop
Minkyeong's Instagram: @soft_seoul