As everyone knows Chiang Rai and Chiang Mai are the 2 most popular cities north of Thailand. Being north it is mountainous so I will say the mountains are very beautiful with resorts there so you could relax in the mountain. I have been ther 5-6 times for work so each time didn't have time to really look around however the most memorable thing I experience is the road between Chiang Mai to Chiang Rai, its awesome, beautiful and exciting. The kao soi there is delicious, its like our curry noodles but the noodles is a little deep fried and crispy.
Sweet & sour smell? Are you referring to tomyam or maybe somtam?