Gibralta - do it on your own. There are small mini buses outside the port that will take you up to the Rock for a fraction of the price and drop you back down in town, the walk back does not take long, 15 mins max.
We only saw 2 monkeys, they must have all been walk about at the other side of the island. St. Michael Caves were worth seeing.
If you have time to stand at one of the view points that overlook the Airport Runway, it is worth watching, when a plane is approaching; pedestrians, cyclists and motorists clear the road, the barrier comes down and the plane lands!!!
The shopping is good, duty free prices.
Next Stop was Toulon in France, we only got off and went about locally.
Next Stop was Italy ( 2 ports) we did Pisa, we took a shuttle bus from the ship and a bus from town to Pisa for 12 euro each return.
Rome:is amazing if it is your first trip I would go with the ship's tour
Sardinia: Has nice country side and the port side of the town is pretty so is the view point at the highest point, plenty of shops, we were there on a Sunday so they were all closed.