Walk off the boat and make for Casemates square. Catch the free bus to the cable car. Go up the rock. Walk to all the sights and walk back down via the castle.
GO TO THE THEATRE ROYAL BAR AND RESTAURANT!!! A great find that we stumbled upon walking back down to Main Street.
We did this all in 3.5 hours. We saw no-one on the rock when walking on foot! Everyone took white minibuses instead.