And it is far more convenient than using train - especially if there is an impromtu local train stike, you can get stuck! We experienced that in 2008 - train from Cannes to Monaco, upon return we found the display board was completely dark - there was an impromptu strike going on... We needed to get back to the ship by 5pm last tender ... At the end, we took bus from Monaco to Nice, then another bus from Nice to Cannes... When we got close to Cannes the road was extremely congested. People on the bus advised us to get off near the train station and walked fast back to the port... On the way I already had thought about we might miss the boat, literally, and how to fly to the next port. Well, due to the train strike causing huge traffic congestion on the roads, the cruise ship's own excursions could not get back to the port either. By the time we planted ourselves in the long tender queue, we saw the Princess tour buses came back one by one, all 4 of them... The tender operation did not finish until 1hr45min after the original scheduled time... Our neighbor who went to Monaco with us but they went to casino we went to the botanic garden, returned to the ship much earlier after they found out casino did not open until 2pm... So they had plenty of time to get back to the ship, and the wife left a worrying message to our cabin phone, wondering if we could make it back in time...
SNCF train service at Cote d'Azur is very notorious for the impromptu strikes especially in travel season!
It was only 1 euro for the bus fare back in 2008. Our neighbor marveled that must be the CHEAPEST long distance bus fare in the world. 
In fact out of the multiple times we visited Cote d'Azur, only 2 were thru land trips, the rest may be 5 to 6 times all were port visits.
Seriously those towns along the Spanish Coast and the French Riviera are all perfect candidates as port of calls for those who take Transatlantic / Med cruises multiple times, as in every year or every other year... far better than use long land trip once and not come back in many years... We prefer to visit them every 1 to 2 years via cruises. 
