The wrath of Bromo is appeased during the annual Kasada festival, when Tenggerese Hindus come to Bromo to make peace with the mountain, and pray for health and good harvests. During this time, local daredevils descend into the crater and use nets to attempt to catch offerings (money, food and even live chickens) thrown down by others above.
It's a risky business and is as dangerous as it sounds – every few years someone slips and the volcano claims another victim. The festival takes place on the 14th day of the Kasada month in the traditional Hindu lunar calendar. Dates change each year, but for the next couple of years, it's likely to fall in June.