This is the decoration at the top of all the Buddhist monasteries and temples. The two deer symbolize Deer Park in India where the Buddha was said to have given his first sermon.
This area of Kathmandu was an enclave for Tibetans, and also, it seemed, for Buddhists. Tibetans fled here from Tibet when the Chinese invaded, and this is supposed to be one of the few places on earth where the culture is still strong.