Your welcome , at Barcelona P&O will put on a free shuttle bus from the ship to the city centre just below the Ramblas and from there everything is easily available . If you want to see the WW2 bunkers on Gibraltar then a P&O tour is advised as it is only a half day stop over in Gibraltar and if you go independantly and you are late back then the ship will not wait for you so better be safe than sorry.Cannes is a lovely place , the harbour is to small for Ventura to dock so it anchors a few hundred yards out and you are ferried in on tender boats and the town centre and shops are virtually right across the road .Cannes is suppose to be a millionaires playground and there is evidence of this by the boats in the marina but you wont need a millionaires bank balance to enjoy yourself there, we just stayed in Cannes but we also spoke to people who visited Monte Carlo and Nice who said they were great places to visit but who wished they had done it independantly rather than expensive P&O tours, so it may be worth your while doing a bit of research first .The only P&O excursion we did was to Rome and is highly recommended , Rome is a big bustling city and it can be quite hard to see everything even though you get a full day to do it in but it can be a very tiring day if your tour involves alot of walking but P&O also do half day tours round Rome where you are virtually on the coach all the time but you do get to see all the sights even if it is through a window, this may suit the more elderly passengers on the ship.