Nikšić  is the second largest city in Montenegro. In Nikšić proper there are a few sites to see but most of the really interesting places are located on the way to or from the city (such as the Ostrog Monastery).
One hour by bus from Podgorica, €3 for one way, frequent busses. Scenic ride.
One of the most popular beers in Montenegro, Nikšićko beer, is brewed in Nikšić. It is definitely a good choice instead of expensive imported beers.