A photo with lots of delightful details which emerge on magnification (see enlarged sections below). Pedestrians and horses walking up Zeppelinstraße reduced to ghostly blurs by the long exposure, people sunning themselves in the square, a man and a woman looking eagerly into a basket (containing a baby?) and, in front of the tram, the shadow of the horse pulling it. That shadow means we can date this to before 1907, when the Potsdam tram network was electrified. (Thanks to my friend in Berlin for that detail).
Today the square is still dominated by the Brandenburger Tor, which you can just see the edge of on the left. However, the park and ornate fountain have gone, replaced with paving and a larger, plainer fountain.
Many thanks to Flickr user Paul Zucchini for matching up the buildings with this Bing maps image.