Can I only eat it in Chiang Mai?
No. It is a signature dish eaten in many northern cities. If you are meeting northern food for the first time in Chiang Mai, a bowl of khao soi is a good start.
Khao Soi · ข้าวซอย
If you are choosing a meal in Chiang Mai, try khao soi. It is a signature northern dish of egg noodles in coconut curry broth, topped with crispy fried noodles. There is fun in alternating between soft noodles and crispy noodles. If lime comes on the side, taste the broth first and then squeeze in a little.

The features are the rich curry broth and the texture of two kinds of noodles. The noodles on top are crispy at first and soften little by little when they touch the broth. If you taste the broth before and after you add the side items, you can enjoy different flavors in one bowl.
Try the crispy noodles on top before they get soaked in the broth.
Khao soi is well known on a Chiang Mai trip, but it is also eaten in other northern cities. Unlike a northern meal with sticky rice and side dishes, noodles and broth come together in one bowl. It is a good pick if you are eating alone or want a simple lunch.
No. It is a signature dish eaten in many northern cities. If you are meeting northern food for the first time in Chiang Mai, a bowl of khao soi is a good start.
There are menus with chicken, beef and other meats. Look at the main ingredient written on the menu and choose what you want. Not every shop uses the same meat.
If you want to read more about the food and the regions behind it, these sources are a good next step. Ingredients and cooking methods can differ from one place to the next.
Sharing image credit: Takeaway · CC BY-SA 3.0