Where the markets are
The two biggest and best-known markets set up on Old Town Square and Wenceslas Square, running from late November through to just after the new year. Old Town Square gets the taller, more elaborately decorated tree and is the more atmospheric of the two, framed by the Týn Church spires and the Astronomical Clock; Wenceslas Square's version is longer and a little more spread out. Smaller markets pop up elsewhere around the city each year, including near Prague Castle.
What to eat and drink
Svařák (mulled wine) is the market's default drink, served in a small mug you can either return for a deposit refund or keep as a souvenir. Food stalls sell roasted chestnuts, sausages, ham roasted over an open flame (pražená šunka), and — everywhere — trdelník, the sweet rolled pastry dusted with sugar and cinnamon. Worth knowing: trdelník isn't actually a traditional Czech dish, and locals mostly leave it to visitors; it's still fun to try once, just don't mistake it for authentic Czech baking.
When to go
Evenings look best, lit up and atmospheric, but they're also when the crowds peak, especially on weekends. If you want the photos without the crowd in them, a weekday morning is your best shot — the lights and decorations are up regardless of the hour.