Bangkok has been ranked as one of the foodiest cities & no doubt it deserves this position. Street food in Bangkok is widely popular just like any other south-east Asian country where people tend to eat a lot more outdoors and that's one of the reason that Bangkok has so many food markets (Ta-laad - in Thai).
In Thai they've a saying which means "Eyes bigger than stomach". The reason is that they really have very delicious food and they tend to order a lot more they can eat. Well I'll list down some common dishes and food markets to eat real Thai food.
Tom Yum Krung
Som-Tum (Green papaya salad)
Dessert (Mango with Sticky rice)
Bangkok also has some famous markets for food -
If you're a foodie person then there is no better place than Khlong Toei in Bangkok. While walking in the small, smelly alleys you could see Thailand from a real perspective. Try some Pork belly with sticky rice, braised pork trotter and intestine (so soft that it will melt in your mouth), don't miss the sticky rice with mango dessert , skinned frog or even live ones if you prefer, pigeon barbeque and crabs of course.
You can find endless varieties of seafood, chillies, fruits, vegetables especially durian. The small, dirty alleys will make you feel happy and proud to have witnessed something special.
Also, check out this video of Andrew Zimmern who goes to Bangkok and his first stop was Khlong Toei market.
Jatu-Jak (Pronounced as Chatu-Chak in Thai)
You can find noodles, pork belly with rice, endless buffet shops, grilled meat balls, fruit shops, ice-cream (believe me you have to try this - it's made of coconut and topped with corns), mango ice-cream and other snacks are easily available here.
Or Tor Kor MarketIt's completely different from the other markets mentioned above. I'd suggest you to bring a camera to take pictures of the fresh vegetables, fruits available in the market. It has also ranked as one of the top most fresh markets in Asia.
As always now it's your turn to go to these places and try these wonderful dishes to know about the diverse Thai culture. Remember that's the best way to learn Thais and make new friends.
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