You can climb the mount Srd by the cable car and watch the prettiest sunset in your life with the view and good food in the restorant Panorama. If you like adrenaline I recommend you to try Dubrovnik zip line.
Watch a sunset on mount Srd
I recommend you to go on a beautiful historical walk thru Dubrovnik city walls.
Dubrovnik City Walls Walk - Useful Guide & Top Tips