were installed on two sites to allow future endeavors to sample borehole fluids. In July and August 2018, the French TRANSECT cruise was conducted on L'Atalante utilizing the ROV VICTOR to collect a variety of measurements and samples. The following month, American cruise AT42-01, nicknamed Return to the Lost City, was undertaken to revisit the vent field after many years, featuring many members of the original discovery team in 2000. Photographs, ambient gases, cells for cultures, rock, vent fluid, and ambient seawater samples were collected using the ROV Jason II and a CTD Niskin rosette. The mission's key objectives were to collect biological and geochemical samples for researching sources of energy for microbial life. They also followed up on the 2015 borehole expedition by attempting to sample from the drilled holes for access to residual fluids. Geography Lost City is located in the North Atlantic Ocean on the seafloor mountain Atlantis Massif, which is approximately the size of Mount Rainier. The site is described as a long-lived vent field, estimated to be older than 120,000 years by radiocarbon dating the oldest chimney deposits of the field. However, this is significantly younger than the age of the Atlantis Massif itself, which may be as old as two million years. Lost City is located on a shelf approximately below the massif summit at a depth of around , with an approximate area of . The massif itself may have originated in a similar manner to many other ocean core complexes. Lost City is a location dominated by steep cliffs to the south, chimneys, and mounds of carbonate material deposited from chimneys that collapse as they age. Breccia, gabbros, and peridotites are dominating rock types as one maneuvers away from the field, which are prone to mass wasting as the bathymetry steepens. Mass-wasting events of the past are evident by bountiful scarps on the slope of the massif. Rubble tends to accumulate at areas no steeper than 60 degrees bounding the field, and can undergo lithification depending on how far it is located from Lost City. Of the 30 active and inactive vent chimneys, Posidon is the largest and most-studied within the vent field. Posidon stands about tall and wide and has numerous orifices venting hot fluids. The vent nicknamed Beehive, for its distinct shape upon discovery, is about one meter tall and located on the south side of Posidon. Furthermore, the IMAX