To reach the Belvedere Hotel in Medulin, the best option is to fly to Pula (there are daily flights from Germany (Frankfurt, Munich), France, Italy), and then a taxi or Uber to the hotel which is located at about 10 km from the airport.
The other option is to fly to Zagreb (direct flights from major cities), and to take a bus to Pula. There are about 10 buses everyday between Zagreb and Pula, it takes about 3.5 hours (280 km) and then a taxi or a Uber to the hotel.
Alternate routes include buses from Venice (4 hours), Trieste (2 hours), Ljubljana (3 hours).