Seoul Metro

Naver Map is a must when taking the subway.

You can't use 50,000 won bills. It's quite a hassle. You can't even ride the bus without a T-money card, so it's really inconvenient if you don't know that. You'll be in trouble if you don't research properly before you go! I recommend everyone to do their research thoroughly before visiting!

The system of having to rent a transit card for 500 won every time, then returning it at the station where you get off to get your 500 won back, is such a hassle.

I think the subway is easy to understand.