Only a few ships still make the journey, the best known being the Queen Elizabeth 2. Depending on the number of ports of call, the average trip is roughly 6-14 days, although some are longer. Ships traveling from North America depart from several cities, including New York, Boston, Ft. Lauderdale and Miami. They terminate their voyage at different locations, including Barcelona, Venice, Lisbon, Copenhagen and Genoa. In between, their stops are determined by the length of the trip and the cost. For example, you can take the Royal Princess on April 11,2000, and take a nice 19 [day] cruise to Barcelona. Your port of departure is Buenos Aires, and in between, you'll visit Montevideo, Rio de Janeiro, Recife, Dakar, Madeira, Casablanca, Gibraltar…not a bad way to get to Barcelona.
There is more here. I've also been trying to Google how planes traversed the Atlantic during the early years of WWII, although without success.
I believe that volcanoes are an underrated ecological problem and that this story still is being underreported. Events could prove me wrong in very short order, but I am reminded of the financial crisis, and the associated explanations from governments and the financial sector itself, around the time of the Bear Stearns collapse.