Wikipedia
Ridván
Riḍván ( ; Persian transliteration: Riḍván, ) is a twelve-day festival in the Bahá'í Faith, commemorating Bahá'u'lláh's declaration that he was a Manifestation of God. It begins at sunset on April 19 and continues until sunset, May 1 (in 2016.) On the first (April 20), ninth (April 28) and twelfth days of Ridván (May 1), work and school should be suspended.
"Ridván" means paradise, and is named for the Garden of Ridván outside Baghdad, where Bahá'u'lláh stayed for twelve days after the Ottoman Empire exiled him from the city and before commencing his journey to Constantinople.
It is the holiest Bahá'í festival, and is also referred to as the "Most Great Festival" and the "King of Festivals".