Germany’s forces were turned back for the first time in world war 2 at:

At Moscow.

Explanation:

Until December 1941, the German army had advanced in Europe in both the East and the West, winning one victory after another. After the invasion of the Soviet Union on June 22, 1941, the Wehrmacht and its panzer divisions had penetrated deep into Soviet territory, conquering all major cities and towns in its way to Moscow. In December, German units camped and took positions on the outskirts of Moscow.

However, the Soviet Red Army managed to build and keep a successful defense of the Soviet capital thanks to fresh reinforcements arrived from beyond the Urals region. The Soviet high command also managed to launch a counteroffensive that pushed away the German from Moscow and forced them to retreat in the 1941-1942 winter. Russian efforts were also aided by the freezing weather as German troops did not have proper clothes and equipment for the winter.