Get your sweat on: Chiang Saen (3 days. A lot of walking.)
A 4 hour drive from the central northern hub, Chiang Mai, will get you to the Golden Triangle. Here you can take a boat trip along the Mekong Delta and pop over to Laos briefly. But since you’re this far up north, you should take a hill tribe trek to see the stunning Thai wilderness and meet hill tribes who still live out in the jungle. Wear grippable shoes, wear long pants as you will be striding through the bush, bring mozzie repellent, a head torch would be great when searching for the loo in the dead of night and be prepared for creepy crawlies. It will be quite hardcore in this heat for those who aren’t particularly fit, but if I can survive it (barely) then you can too!