Prijepolje is a multi-ethnic town that was considered peaceful even in time of ethnic conflict in Bosnia and Herzegovina.
One day train ("Tara") and one night train ("Lovcen") take six hours from Belgrade via Rakovica (for Belgrade suburban lines) and Bijelo Poljea, and continue from Prijepolje to Podgorica and Bar; they're chronically late. The day train is cancelled at least until mid-Dec 2021. In Belgrade for some years these trains departed from Topcider, the dreary motorail terminal in the southern burbs, but they now run from Centar station.
While you are in Prijepolje, you can rest among many seating places carved from wood and other small oasis such as artistic benches and eco parks made by local activist and artists.