What a Tshechu is
A Tshechu — literally "tenth day" — is a religious mask-dance festival held in the courtyard of every major dzong, on dates fixed by the Bhutanese lunar calendar. It's a public commemoration of the deeds of Guru Padmasambhava, the 8th-century saint who brought Vajrayana Buddhism to Bhutan.
These aren't performances put on for tourists. They're working religious rituals, attended by entire villages dressed in their best gho and kira, with the dances themselves believed to bless those who watch. Tourists are welcome; the calendar is the calendar.
Every Tshechu runs three to five days. Major ones — Paro, Thimphu, Punakha — pull tens of thousands of pilgrims. Smaller valley Tshechus might have a couple of hundred. We can put you at either, depending on what you want.