Namdaemun (also called 'soong-nae-mun' when talking about just the gate - 'mun' means 'gate' or 'opening' in Korean) is both a historical site and a famous market. The 'Great South Gate', as the name can translate to, was one of the four main traditional gates into Seoul and makes for a great photo-op just outside one entrance (towards the west side) to the market.

The market itself is one of Seoul's oldest, and you can find nearly anything here. Be prepared to wander, get lost, bargain heavily, and see some great sights. The market is mostly open-air - keep this in mind if the weather is less than great for walking.

Hours: It's pretty much 24/7, with the night market being especially active.

Transportation: Take subway line 4 (the light blue line) and get off at Hoehyeon Station, or just tell the taxi driver 'nam-dae-mun' (and it's NOT 'nam', like 'dam'! The 'a' in 'nam' is pronounced more like 'pond' or 'palm', 'dae' sounds like 'day', and 'mun' sounds like 'moon'.)

Website: For the market: http://map.indm.net/ (very fancy site)