Central Nizhny Novgorod is compact enough to walk around, and a car-free pedestrian zone, ul Bolshaya Pokrovskaya, links the main square, pl Gorkogo (пл Горького), to busy pl Minina i Pozharskogo (пл Минина и Пожарского), near the kremlin.
Both the bus and train stations are located on the western side of the Oka River, about 3km from main sights (which are all situated on the eastern side). Buses and marshrutky run from the train station to both hubs on the eastern side: pl Gorkogo and pl Minina i Pozharskogo. The metro has a useful link between pl Gorkogo and the train station.
Uber ride-share service (www.uber.com) operates in Nizhny and rates are significantly cheaper than standard taxis.