Dubrovnik

We have just booked Lyra into the ACI Marina outside Dubrovnik for 2015/6. This will give us the opportunity to explore the southern half of Croatia this spring/summer and Montenegro this autumn. We are also keen to explore Bosnia (by car) and Dubrovnik will be  a good central place to do this from.  It's also a little easier to fly into Dubrovnik off-season than Zadar , where flights stop entirely for the winter. 

Any recommendations of 'must see' places in southern Croatia warmly welcomed..