The world's longest cruise is being offered by Viking Ocean Cruises. It lasts eight months and includes explorations of the world's most thrilling landscapes, from the Great Barrier Reef to the Amazon rainforest. But only lottery-winners and plutocrats need apply for the entire trip - you can join the cruise for as little as a week at a time. To book a more standard room for the whole trip, prices start at £66,990, though, it has to be said, for top dollar, you do get the experience of a lifetime, writes Lesley Bellew. Unless your travel bucket list includes a visit to the International Space Station, you are likely to tick off everything on it.