Changangkha Lhakhang is one of the oldest monasteries in the Thimphu valley. It built in the 15th century by a descendant of Lama Phajo, the man who spread the sect drukpa kagyu in Bhutan. The main statue at the temple is of Avalokiteswara (the eleven-headed Buddha manifestation with 1000 arms and 1000 eyes). You have to walk to reach it. The temple courtyard offers good views over the city of Thimphu.