Myeongdong is one of those well-worn tourist destinations that you just can't avoid if you are visiting Seoul, even for those who turn up their nose at anything found in a travel guide. Even for those who aren't shopping pros, walking through Myeongdong is a visceral experience without ever stepping into a single store as the car-free streets are always packed and the people and window watching is reason enough to visit.
The main section of Myeongdong isn 't very large so it's easy to experience in a few hours if you don't dawdle but you could spend a whole day easily if you intend to fully experience all that Myeongdong has to offer which includes the historic Myeongdong Cathedral and a handful of large department stores such as Lotte, Shinsegae, Migliore and more.
Shopping tip: For those looking for luxury or high-end, go to Garosugil or other more quiet shopping neighborhoods like Apgujeong where you can caress your Louis Vuitton in peace amongst the civilized. Myeongdong is for bargain hunters and mid-range shoppers who want to be amongst the shopping hordes, community shopping if you will. It also offers endless options for Korean skincare and make-up lines which are highly coveted around Asia as Koreans are known to be skin and beauty obsessed.
Stick around til 5pm when the street carts peddling tteokbokki, skewered fish cakes and such begin setting up, providing much needed sustenance to replace the calories burned by marathon shopping sessions.