I understand wanting to go by foot, but I suggest the UBahn. It’s two short stops. Otherwise you could walk this street past the seedy Hotel National, the Colour Hotel, the sari shop and Arabic grocery. After the intersection, you’ll reach a sandstone bridge. Set off across it until you find the stairwell down to the promenade, and follow the river eastward. I can’t vouch for the safety of the riverside at night, never having ventured it. The linden trees are almost bare. Keep walking about 15 minutes until you see the lights of the Christmas Market on the left. Somewhere there are stairs back up to the street. You can’t miss it, the smell of spilled wine, the sound of an accordion, the flocks of people. If you pass beyond the Eiserner Steg footbridge you’ve gone too far.