Definitely walkable. I did that a week ago to get back to Myeongdong from Insadong. Only took about 15-20mins. Just use google maps to help you. You may use Cheonggyecheon stream to help you along the way.
It is close, but not walking distance. Take a cab and it will cost you only 5,000 KRW (less than US$ 5.00).
Yes. Normal walking speed and good weather, probably around 15-20 minutes walk. If you know the way of course. Part of this walk may pass along a small stream walking path. Have fun.
If you like walking, yes it’s a flat, safe, easy walk of about 20-25 minutes. It’s also easy to hop on a bus near Jogyesa Buddhist temple or Jongno 2-ga and ride it one stop south
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