Lucia looks like an absolute classic of a nominally Christianized Pagan light festival, with a procession of girls dressed in white robes singing and carrying candles near the darkest part of the year. Screwy was cynical when I described it as such, though, and it turns out (see the Wikipedia article linked above) that it is in fact too good to be true; it's a relatively modern invention, based on a Romantic idea of what Pagan festivals might have been like. There seem to be some older roots though.
Anyway. The prettiest girl is elected Lucia, and she wears a crown of four candles, so it seems like there are bits of Christingle in there too. The other girls wear wreaths of fruit and flowers. While listening to them sing, one eats certain special foods. Lussekatter are special kind of bun, flavoured and coloured bright yellow with saffron (to encourage the return of the sun by sympathetic magic, apparently). They are shaped like a figure of eight; it takes a lot of imagination to see why they're described as Lucia's cats. My Swedish teacher suggested they look a bit like cats that have been run over and squished flat by a steamroller! Pepparkakor are a really tasty kind of ginger snap, very thin and gingery, which I have been happily getting addicted to over the past few weeks. Some of them actually do have pepper in as the name would suggest, others are just spiced but not overly sweet. Glögg is essentially mulled wine, I think; apparently there is a different flavouring theme each year, and one puts almonds and raisins in the wine.
So in our case, the Lucia procession was formed by some high school kids. Traditionally it's girls only, but these days boys are very often involved, borrowing bits of other seasonal traditions such as dressing up as Christmas elves or something called "starboys" which I think dates back earlier than Lucia itself. It's particularly useful to include the boys if you're trying to sing SATB, as this group were! I really wish someone had warned me that the starboys' costume consists of white robes and, get this, tall pointed conical white hats... When they made their entrance they momentarily reminded me of the Inquisition, which rather spoiled the emotional effect. Gleep.
Anyway, once I recovered from that shock, it was a very sweet little celebration. I'm spoiled by 20 years in Cambrige and Oxford; my assessment of the singing was that they were trying for stuff that was a little technically ambitious for untrained singers. They had a lot of polyphony with complicated rhythms and harmony, and their execution was hit-and-miss, pretty when it worked but rather ragged a lot of the time. Then someone mentioned that they are in fact not untrained, but pupils at a specialist music school.
Nobody had much idea what Lucy was actually canonized for; someone suggested preferring to be blinded rather than give up her faith, another that she was burned at the stake protecting her virginity. But they clearly don't really regard it as a Christian festival!