San Juan is celebrated in Bolivia every year on 23 June and is said to be the shortest, and usually the coldest, night of the year.
Typically bonfires are set and people gather all night to sing, play guitar, eat and spend time together, warming by the fire and hoping this really will be the shortest, coldest night of the year so as to get it over with once and for all.
Most bonfires were set in the streets, even in large cities. However, the next morning there was so much smog that authorities have put a stop to that and are now fining anyone who sets a bonfire in town. For environmental reasons, bonfires have been banned in most major cities of Bolivia.
Still, hot dog sales go through the roof as people traditionally roast "panchitos" as they are called, along with pigs, goats, and other animals. The "parrillada" or "churrasco" (as barbeques are called here) usually include hot dogs or sausages, lots of chicha or other alcoholic drinks, and a guitar somewhere in the crowd.
In La Paz, the day after San Juan used to be a holiday as well - not so much because it really is, but because the amount of smoke lingering in the air made it impossible to go outside, much less get to work. However, now that's all been "cleared up" with the bonfire prohibition.
One tradition in La Paz is that anyone who can, will stay up all night, and eat "fricassé" (a thin broth with pieces of pork, ground red chili pepper and chuños, which are dehydrated potatoes) at about 5:00 a.m. in order to warm up.
In some rural towns like Porongo dancers will walk on hot coals to show the spirits they are macho and unafraid of the cold or any other malice they may want to bestow upon them. But mostly, people will just use this as an excuse to combine weathering the cold with having yet another party. So if you're ever in Bolivia in June, bring your jacket and a skewer - there's room at the hearth for everyone. If you're traveling, you might as well make the most of it and enjoy.