Does anyone have experience traveling from Alpe di Siusi (Italian Dolomites) to Rijeka, Croatia? With car, how long of a trip is it? Am I better off to ditch the car and take public transport? If so, what is the preferred way (e.g. train, bus, plane)?
Better plan on driving - from the Seiseralm eastward that's just about the only transportation (unless you know your way around Italian bus schedules). Train travel along the Adriatic is spotty, but you may want to look at schedules from Trieste on. Most trains in Slovenia go farther inland from Ljubljana via Zagreb. But you may check with the experts at tripadvisor.com who may have some better info.
Most European vacationers to Rijeka come by car.
We went the opposite direction, traveling from Rijeka to Venice two years ago. We took a bus from Rijeka to Trieste & stayed overnight (there's a hotel booking office adjacent to the train station-- it's a beautiful town, well worth an overnight stop). Then it was a quick train trip into Venice next morning. You could possibly even bypass Venice -- I'd check bus/train connections from the Dolomites into Trieste.