Graves are cleaned and people pray to their ancestors. It's a time to think about the past and departed loved ones. Flowers are placed on graves all over Japan.
It's also common to light lanterns and candles on the family grave site.
Obon isn't just a sombre affair. It's common to celebrate the reconnection with one's ancestors. There are obon festivals all over Japan (to which the dead are invited). Obon festivals vary greatly from region to region. They often incorporate traditional Obon dances such as the massive Awa Odori in Tokushima.
The days of Obon aren't public holidays. Nevertheless, it's common for companies to give employees holidays for obon. It's also common for people to use their personal holiday allowances during this time.
Obon is the second busiest travel time of the year in Japan (after Golden Week). The prices of travel packages skyrocket. Highways, public transportation, beaches and onsen are pushed to capacity.
Obon is always three days. There are different start dates that vary by region: 15 August, 15 July or the 15th day of the 7th lunar month (date varies by year).
Obon is perhaps Japan's most important religious holiday. It has been spread all over the world by Japanese immigrants. There are big Obon festivals in multiple locations in the United States and Canada, South America and Asia.