Koper, Izola, Piran and Portoroz. All of these cities have rich history and interesting old town centres except Portoroz that is a little bit more modern with many hotels. One of most scenic bays on Slovenian Coast is Moon's Bay (Mesecev zaliv) which is located in Strunjan Landscape Park. I would suggest also to see Secovlje Salt-pans where you can still see how to make salt on the old fashioned way. Of course there are also other interesting places worth to see. One of them is for sure Garden of Cacti on Cape Seca where you can see a lot of different cacti.