Antarctica is the least-visited continent. Until about 1820, no human had seen it and it is doubtful whether anyone landed on it before 1894 or spent a winter ashore before 1899 (Stonehouse 1994:195). Today parts of the continent and several of its offshore islands provide the settings for scientific studies and for some of the world's most remote tourism operations. Between mid-November and early March, when ice conditions are less severe, the region is visited regularly by tourists aboard cruise vessels. Airline passengers view the scenery through the windows of airplanes, which overfly parts of the continent. During the 1990s, the number of voyages increased as tour operators responded to a growing demand for Antarctic tourism.