Red are my corrections.

My Trips in 2013

I travelled to Thailand and Combodia last month. It's was really a happy experience for me. In Thailand, My favourite city is Chiangmai. It's a city in northern Thailand. It's fit for people to relax themselves and empty their mind. if you have a busy job work just like me, Chiangmai is a good chioce choice for you to spend your holiday. when i was there, I was lucky as they were for celebrating the Sky Lantern Festival. i was so moved when i saw see thousands of sky lanterns rise together. It was [1] that's the most beautiful and romantic scene.

[1] 'It was' is past tense as you are referring to something that has happened. There are other ways you could phrase this as you might be suggesting this to someone by making it future tense. Example: It is the most beautiful and romantic scene you would ever see.