Gwangjang Market is loud and packed but that is the fun of it. Go before noon if you want a seat, and bring cash because a few stalls still do not take cards.
Seongsu is my favourite walk in Seoul. Most roasteries have English menus and the staff were happy to explain the beans, and there are plenty of quiet seats on a weekday morning.
Myeongdong is crowded but the tax refund kiosks are easy to find and most shops accept cards. Come on a weekday evening if you hate queues.
Itaewon at night is the easiest place in Seoul to eat when you do not speak Korean. Most menus have English, and the halal places near the mosque were a lifesaver for my family.

Seongsu Cafe Street
ซองดงกู

Itaewon Street
ยงซานกู

Gwangjang Market
ชงโนกู

Myeongdong Shopping Street
จุงกู

Mangwon Market
มาโพกู

Dongdaemun Design Plaza
จุงกู

Garosu-gil
คังนัมกู

Gyeongbokgung Palace
ชงโนกู

Samcheong-dong Street
ชงโนกู

Namdaemun Market
จุงกู

Yeonnam-dong Gyeongui Line Forest Park
มาโพกู

Apgujeong Rodeo Street
คังนัมกู

The Hyundai Seoul
ยองดึงโพกู

Lotte World Mall
ซงพากู

Hongdae Walking Street
มาโพกู

Euljiro Nogari Alley
จุงกู

Insa-dong Ssamziegil
ชงโนกู

Bukchon Hanok Village
ชงโนกู

Ikseon-dong Hanok Street
ชงโนกู

Cheongdam Luxury Street
คังนัมกู