Summer
Monsoon lasts from June to August and though outdoor expeditions and activities are often limited due to the rain, you can still visit some monuments and have great indoor experiences like visiting a happening café in town and sipping a hot brew while reading a book or you can use the extended indoor times to make friends with the locals. There is also some great music and entertainment in happening spots like some of the well-known bars in town where you get to mix around with a cross section of the Bhutanese society especially the more artistic types if that is your thing.
Winter in Bhutan lasts from December to February in Bhutan. It is pretty cold in the northern belt and you cannot go for treks because the passes are blocked with snow but you can opt for the other activities like visiting monuments, the bazaar, relaxing in a spa, shopping for souvenirs and yes, the famous Bhutanese home stays where you will be welcomed into the hospitality of a Bhutanese family. Enjoy the warmth of the hearth as well the household as you make yourself at home.