The Portorož Auditorium is the largest events and conference venue on the Slovenian coast, built in the 1970s and extensively renovated since. It hosts the Slovenian Film Festival (Festivala slovenskega filma) each autumn, when the Slovenian film industry descends on the town for its equivalent of Cannes — a scaled-down but genuinely lively affair that brings filmmakers, critics, and cinema-goers together for a week. Throughout the year the auditorium hosts international conferences, concerts, and theatre performances.
Check the programme before you visit — if something is on, it's well worth attending, both for the performance and for the chance to see how a small country with a serious cultural tradition does things properly.