Ljubljana likes to party hard, and party late. The place goes positively Mediterranean during the summer, with cafés, bars and restaurants staying open well into the early hours as locals and visitors alike simply forget to go home. All of the city’s squares bustle into the early hours too, with the city’s main square, Prešernov Trg, often still packed with revelers until 03:00. Indeed, Prešernov Trg is something of a focal point for Ljubljana nightlife, with most of the city’s best bars, clubs and cafés nearby.
Also note that this is by and large a very easy going city, and is no such thing as a no-go zone. Do not worry about walking home on your own late at night.