Map of Northern Thailand
Northern Thailand is much more than a day trip. A traveler could spend weeks seeing all that is Northern Thailand and not be bored.
Chiang Rai alone is worth several days. As a center for trekking the hill tribe areas, Chiang Rai has nature galore. Plan a visit to Wat Rongkhun (use a browser with translate tool) AKA the "White Temple".
Sample the outstanding roast chicken from one of the nearby restaurants that founded that village.
Chiang Mai, of course , is a much larger city. Chiang Mai province is Thailand's largest.