Traveling in trunks is a form of transportation that has been used for centuries. It involves packing items into trunks and then loading them onto a vehicle, such as a train or boat, for transport. This method of travel was popular during the 19th century, when people would often take long journeys across continents. The term 'travel in trunks' is derived from the fact that the trunks were used to store and transport items during these trips. The crossword solution for this term is 'SWIM', which is an apt description of the activity, as the trunks were often loaded onto boats and ferried across bodies of water.