The festival occurs every year just after the Chinese New Year in a small town called Yanshui. Nothing else happens there besides this insane festival. To get there, the best way is to take the train to XinYing station, then take the free shuttle bus. Getting hope is a little harder since the train is usually shut down by then, but you can generally take a taxi back to Tainan for about $30 or $40 bucks.
To attend the festival you need a full faced motorcycle/scooter helmet and a towel. Tape the towel like a curtain around the bottom of the helmet. If you don't, a firecracker could shoot up into the helmet and explode. That happened to a guy I knew on two separate occasions in years past.
They also recommend you wear gloves (taped shut to your clothes), and long pants with taped down ankles (so the rockets don't go up your pants). I would recommend the full gear because it hurts like hell if the rockets peg your skin. I had a friend who went in nothing but a cotton flannel shirt and a bolo hat (with a pair of jeans) and he was fine. So it's up to you really.
If you don't have a helmet, you can buy them for a relatively good price there, but the towel and tape can be hard to find.
Although stories differ, this festival is either to welcome the Buddhist Gods back to Earth after the new year, or scare away a foot disease that used to plague the country/city. And how do they scare away the spirits? By lighting impressive firework displays, and shooting small rockets (by the thousands) into the crowds that come to celebrate every year.
The beehive rockets are like angrily little bottle rockets that are bound together by the thousands and put into a large box. The boxes are usually about 5 feet tall and 5 feet wider or wider. Rockets shoot from both sides and in every direction. Years ago the tips were ceramic, but to make it safer, and to keep the tips from embedding into people's skin and exploding, they changed to plastic tips in recent years.
Essentially, you walk around the town and get shot by fireworks. You have to be ready at any time. Each house or temple group makes their own box(es). Before they are going to set one off, they light a large display that shoots straight into the air. The mob walks through the streets of the small town and stands in wait... to be shot.
In the streets, groups of reckless young men who are trying to prove their strength/coolness light long ropes of firecrackers and drag them around in the street. They whip the firecrackers around there head and eventually into the crowd.
The super badass guys wrap themselves in strings of the firecrackers and then set them off.
If you can, stay until the very end. That's when they bring out the huge box and set of the rockets that are about double the size. The final session lasts much longer than the others and was my favorite part.
Keep your eyes open and watch the fireworks bounce and explode off your visor. Make sure you have a clear one because it's hard enough to see with all the smoke anyway.