Wikipedia
Indra Jātrā as it is most commonly known or Yenyā ( Nepal Bhasa: येँयाः) is the biggest religious street festival in Kathmandu, Nepal. Yenya means "Kathmandu festival" in Nepal Bhasa. The celebrations consist of two events. Indra Jātrā is marked by masked dances of deities and demons, displays of sacred images and tableaus in honor of the deity Indra, the king of heaven. The other event is Kumāri Jātrā, the chariot procession of the living goddess Kumari.
Family members deceased in the past year are also remembered during the festival. The main venue of the festivities is Kathmandu Durbar Square. The celebrations last for eight days from the 12th day of the bright fortnight to the 4th day of the dark fortnight of Yanlā , the eleventh month in the lunar Nepal Era calendar.
Indra Jatra was started by king Gunakamadeva to commemorate the founding of the city of Kathmandu in the 10th century. Kumari Jatra began in the mid-18th century. The celebrations are held according to the lunar calendar, so the dates are changeable.