Glühwein (mulled wine - though literally 'glow wine') is one of the German Christmas market staples, made by heating red wine with spices (usually cloves, cinnamon and allspice, though there are many variations...I like to use cardamon myself), citrus fruits and sugar.
Along with paying for the Glühwein, you'll be asked to pay a Pfand (deposit) for the mug it's served in - you can either return the mug and get the money back, or keep the mug. This one's coming home with me!
A variation on Glühwein is Feuerzangenbowle (fire tongs punch). To make it, a cone of sugar has rum poured on it, before being set alight and allowed to drip into the punch below. The Feuerzange is what's used for holding the sugar - it would originally have been a pair of tongs like those used for grabbing coals from the fire, but now tends to be a specially designed holder.
This is the Feuerzangenbowle stand at the Nostalgischer Weihnachtsmarkt (nostalgic Christmas market) behind the Opernpalais (opera palace) on Unter den Linden. You can see the cones of sugar lined up above the steaming punch bowl, ready to add their rum-drenched sweetness to the mix.