Evening prayers at a Buddhist Monastery is something you should do at least once on a tour of Bhutan. You will witness monks chanting traditional prayers, helping them prepare for meditation.
If anything, witnessing Buddhist chanting is slightly hypnotic and you can sit in for as short or long a time as you want. Do ask whether you can take photographs, and generally you will not be able to use flash or take photos towards the alter.
It looks like you are in the USA
Would you like to: