I'm now in the process of updating this for 2015 - it's mostly done now, but bear with me!
When to go
The major Christmas markets in Berlin open in the last week of November and are open right up until Christmas itself, with some open into the beginning of January (Berlin's also a popular destination for New Year's Eve celebrations, though bear in mind that some accommodation prices go up quite a bit at that time).
December 6th in Germany is Nikolaus - St Nicholas's Day - when children traditionally put out their boots to be filled with goodies by St Nick...though if they've been bad, they may get a stick (called a Rute) for their parents to beat them with instead! If you're staying in a Berlin hotel on the night of the 5th, you may find you get a small gift, like a chocolate Weihnachtsmann (Father Christmas) left for you by your door. I've not noticed them giving out sticks, though...
What to expect
The Christmas markets have stalls selling a variety of traditional (and less traditional) gifts and decorations. Particularly common to see are wooden ornaments from the Erzgebirge in the east of Germany, like Nußknacker (nutcrackers, like the rather fearsome fellow in the picture up above - not things that are really designed for actually cracking nuts with) and Räuchermänner (smoking men - wooden men which you put an incense cone inside, making smoke come out the mouth). Also common to find is Glühwein
(mulled wine), and its rum-laced cousin Feuerzangenbowle - perfect for the cold days!
There'll usually be food stalls too - you'll most likely find at least one selling Bratwurst, often alongside the Berlin speciality the Bulette (which you could either see as a big flat pork meatball, or a bunless pork burger). Gulaschsuppe (goulash soup) is worth looking out for, as is Berliner Kartoffelsuppe (Berlin potato soup), both of which are usually not particularly expensive, but very filling.
If you're after something more on the sweet side, you'll usually find a stall selling Schmalzkuchen, which could be literally translated as 'lard cake' which sounds disgusting. It's actually small squares of deep fried dough, almost like little doughnuts. It's served in a cone of paper, covered with icing sugar, which means it can be hell to eat if you're wearing dark clothes (but very entertaining for the stallholder who's just emptied half his pot of icing sugar onto your Schmalzkuchen). Another thing you'll probably see are the round balls of deep fried dough known as Quarkkeulchen which, when they've been freshly fried and are still warm, are great on a cold night.
What to wear
The weather in Berlin does get quite cold during winter. It's common for temperatures to drop to well below 0°C in December, so it's worth packing plenty of warm clothes...or buy some in Berlin - the Germans know a thing or two about winter clothes! Either one thick jacket or several layers is a good idea, and I always like to have a nice pair of gloves and a warm hat too.
Snow isn't unheard of either, especially later in the month, so you might get at least a small taste of a white Christmas on your visit...no guarantees, though! Beautiful though snow is, it does mean it can get a bit slippery underfoot, though pavements on larger roads tend to get swept and gritted quite regularly. Packing a nice warm pair of shoes or boots with good grips is a good idea!
On the flipside, in a milder winter, it can rain - I like to keep a small umbrella in my bag just in case.
The Christmas Markets (see Christmas markets map)
There are markets right across the city centre - amongst others, there's one on Alexanderplatz, one in front of the Rathaus, one by the Opernpalais on Unter den Linden, one on Potsdamer Platz and one on Breitscheidplatz (around the Kaiser Wilhelm Gedächtniskirche). Those ones are all free to visit; there's also one in Gendarmenmarkt which charges a small entry fee. They generally stay open until well after the shops have closed (often around 9 - 10 at night), so it can be a nice way to end the day, plus the atmosphere is just that bit more special (and the Glühwein seems that extra bit more warming) after dark.
Of course there are many more all over the city (between 50 and 70, depending on who you believe), but hopefully this small selection will serve as a taster (plus they're good if you're only going for a short time and want to see all the sights as well). If you're viewing this via the front page, you might want to click the article's title to take you to the single page view, where you'll be able to see a whole set of handy Google Maps links at the bottom to help you find these markets, of you can follow this link to see them all on one handy map.
The Alexanderplatz market has the advantage of being very close to the station, as well as being close to the shops around Alexanderplatz, which you might find useful for Christmas shopping (and I personally prefer the Galeria Kaufhof on Alexanderplatz to KaDeWe, if I'm wanting a big department store).
It's open from November 23rd - December 27th 2015.
Open daily from 10am - 10pm (but 10am - 4pm on December 24th).
Almost blending into the Alexanderplatz market is the 'Wintertraum am Alexa' (winter dream at Alexa), which stretches along Alexanderstraße to Jannowitzbrücke, along the side of the Alexa shopping centre (the bizarre pink building on the southern side of Alexanderplatz). There's also a big funfair at the back of it.
It's open from November 23rd - December 23rd 2015.
Monday - Friday 2pm - 10pm, Saturday and Sunday 12pm - 10pm (times for 2015 hadn't been released at the time of writing, so these are from 2014)
Alexanderplatz is a major transport hub, so there's a huge choice of ways to get there - S-Bahn (S3, S5, S7/75), U-Bahn (U2, U5, U8), tram (M2, M4, M5, M6, M8), bus (TXL, 100, 200, 248) and regional trains (RE1, RE2, RE7, RB14).
The market by the Rathaus
, known as Berliner Weihnachtszeit, is of course also close to Alexanderplatz, so you can always visit the two, plus take a wander through the nearby Nikolaiviertel, which you might also find good for gifts.
The Rathaus market also boasts a 50m high ferris wheel, which promises impressive views, though stood next to the 368m high Fernsehturm, it's hard not to think of it as rather small!
It's open from November 23rd - December 29th 2015.
Monday - Friday 12pm - 10pm, Saturday and Sunday 11am - 10pm (closed all day December 24th, then open 11am - 9pm on the 25th, 26th and 27th, and 12 - 9pm on the 28th and 29th)
The The Nostalgischer Weihnachtsmarkt
(nostalgic Christmas market) is, in turn, not all that far from the Rathaus. It's now on Schloßplatz, having moved from its previous regular location by the Opernpalais.
It's open from November 25th - December 27th 2015.
Monday - Thursday 12pm - 9:30pm, Friday - Saturday 11am - 10:30pm, Sundays 11am - 9:30pm (closed December 24th, then open 11:30am - 9pm from the 25th - 27th).
I've mentioned the Weihnachtszauber market in Gendarmenmarkt before. Unlike most markets, they charge an entry fee (though still only 1 euro) and a lot of the things on offer are more expensive, but I think it's worth a look. It's particularly good for arts and crafts, and a lot of the food stalls are run by nearby restaurants and hotels. Of course, it's within walking distance of the Opernpalais, so if you fancy doing a market crawl, you can go all the way from Alexanderplatz to Gendarmenmarkt and not be away from a Christmas market for more than about 5 minutes! If you don't fancy the walk, the U-Bahn stations Stadtmitte (U2, U6), Französische Straße (U6) and Hausvogteiplatz (U2) are all close by (the exit from the U2 platform at Stadtmitte is the closest of the lot).
It's open from November 23rd - December 31st 2015 - they also hold a New Year's Eve event there.
Open daily 11am - 10pm (closing at 6pm on December 24th and 31st; entry to the New Year's Eve party on the 31st, from 7pm - 1am, is €12). Entry is free Monday - Friday 11am - 2pm, apart from December 24th, 25th, 26th and 31st when the standard €1 entry fee applies.
I've never taken to the Potsdamer Platz Christmas market as a market particularly, but it does have a toboggan run and a skating rink!
The Christmas market is open from November 23rd until Decebmer 27th 2015 (the toboggan run and skating rink stay open until January 3rd 2016).
Open daily 10am - 10pm (but 10am - 2pm on December 24th).
I've never taken to the Breitscheidplatz Christmas market either, but that's no reason not to take a look at it if you're in the area anyway (perhaps shopping at KaDeWe, or stopping off for a Currywurst at Witty's). It's very close to Zoologischer Garten station, so like with Alexanderplatz, there are plenty of options for getting there.
It's open from November 23rd 2015 - January 3rd 2016.
Open Sunday - Thursday 11am - 9pm, Friday - Saturday 11am - 10pm (but 11am - 2pm on December 24th, 1pm - 9pm on December 25th and 26th, 1pm - 9pm on January 1st, and there's a special late opening from 11am - 2am on December 31st).
If you want to venture ever so slightly further from the city centre, the Schloss Charlottenburg Christmas Market is nice. Like I mentioned last year, the setting is particularly atmospheric. Along with a nice selection of things to buy (there's even a second stall from Kleinbrennerei Fitzke...), it has three restaurant tents, one selling local dishes from Brandenburg, one selling Austrian specialities and one selling mainly duck and goose-based dishes.
It's open from November 23rd - December 26th 2015.
Open Monday - Thursday 2pm - 10pm, Friday - Sunday 12pm - 10pm (but closed December 24th, open 12pm - 8pm on December 25th and 26th).
Other Christmas activities
If you want to enjoy the more religious side of Christmas in Berlin, the Berliner Dom has services and other events (including performances of Bach's Christmas Oratorio) throughout the period. For Catholic services, you may want to try St Hedwig's Cathedral.
You might also like to look out for the traditional Christmas meal of roast goose, something you'll find in a lot of the restaurants that serve more traditional German food.
December is really a lovely time to visit Berlin (if you like wintry weather, at least!), so if you like the sound of what you've read here, then now's a good time to start planning your trip - you can get some great deals by booking early, and some travel agents, hotels and airlines put on special Christmas offers.
Don't forget to take a look at the Christmas markets map if you want to see where they all are!