Some clarification, there is no ready made continuous upper level walk like the sidewalk on the south bank (Wacker). The buildings front the river and the intrepid pedestrian must weave in and out amoung the bridge ends and skirt along plazas, remarkably this is all open, up to the Chicago School, the building just W of 300 N LaSalle. The upper level deck has no access to Wabash, nor does the mid level, the lower level is closed off. To the west is the plaza for the Merchandise Mart which is a taxi way, but walkable.
To the East the old traffic court has a walkway along the river, and a lower level used by the water taxis.
around a bridge end is the ABA plaza
past the westin, you can walk along the river again at Marina Towers and the IBM plaza, Trump and Tribune will take you a building away.
Historically the old path to the North of the parking garage (now 300) and Helen Curtis (now Chicago School) put you right into the long mall of the Merchandise mart. This path is open once again.