Make sure when you get there, you buy a map which costs 2000 won and collect the stamps. Its very fun because you will start to feel like you are adventuring in the neighborhood maze :) Some of the place with stamps will give you free postcard which you can send right away with only 500 won for international fee and free for domestic. I sent one to my best friend in my country (Indonesia) and it arrived after 2 weeks. definitely worth for my one day trip from seoul ^^