Unknown Loop Streets #4... "N. Post Place"...
Located between Franklin and Wells, I would guess this street came into existence at the time of the construction of Wacker Drive specifically to add easy access to the lower level.
I searched for a street sign at the intersection of Lake Street and N. Post, but there was none. The only sign I could locate was at the other end where N. Post enters Lower Wacker.
The view toward Lake Street from Lower Wacker looking South, along this one block long street.