where the playground used to be 作为一个整体,以前是操场的地方
stand做谓语动词
并且整句句子又是全部倒装句
another new building才是主语
改成正常语序,就成了
Another new building now stands On the other side,where the playground used to be
现在又一栋新的大楼坐落在以前是操场的地方