The society began the way many great Victorian institutions began: with seven men over dinner, talking about geography. The founding members in 1830 were Sir John Barrow, the Admiralty's geographer; Roderick Murchison, the geologist who would name the Silurian system; Robert Brown, the botanist whose name lives on in Brownian motion; the politician Lord Broughton; Mountstuart Elphinstone, the colonial administrator who had governed Bombay; the diplomat Bartholomew Frere; and Admiral William Henry Smyth. They met in the rooms of the Horticultural Society on Regent Street. From there the institution grew with the British Empire, sending out the men whose names became synonymous with Victorian exploration: Darwin, Livingstone, Stanley, Scott, Shackleton, Hunt, Hillary. The expeditions sent back what they found - charts, journals, photographs, specimens - and the RGS kept them.

After several moves the society found its permanent home in 1913, when it purchased Lowther Lodge in Kensington Gore for £100,000. The building had been designed in 1874 by Norman Shaw, one of the great domestic architects of the Victorian age. The same year the society moved in, it lifted its ban on women fellows - a struggle that had run for over two decades. The 1929 east-wing extension, with its New Map Room and 750-seat lecture theatre, was opened in October 1930 by the Duke of York. He would later, as George VI, become king. The lecture theatre is still where the Monday-night talks happen - lectures the society has recorded since 1994 and now streams to its members.

The collection spans five centuries of geography. There is a 19th-century guidebook to Berlin. There are 4,500 expedition reports, a database of 8,500 expeditions stretching to the present. There are over half a million photographs and lantern slides, from Herbert Ponting's photographs of Scott's South Pole expedition in 1912 to the contemporary aerial and satellite work that supplements them. There is a globe-shaped emblem above the door, the unicorn-and-lion shield of the society's royal charter, and a glass pavilion built in 2004 where exhibitions are now held. That same year the society opened these collections to the public for the first time. For most of its history, only members had walked through the Foyle Reading Room. Now anyone who registers can sit at one of those long oak tables and read Livingstone's account of the Nile in Livingstone's own handwriting.

King William IV established the medals in 1831 with a gift of fifty guineas a year, "to constitute a premium for the encouragement and promotion of geographical science and discovery." In 1839 the society converted it into two gold medals - the Founder's and the Patron's. The recipient list reads like a history of exploration: David Livingstone in 1855, the Indian surveyor Nain Singh Rawat in 1876, Ferdinand von Richthofen in 1878, Alfred Russel Wallace in 1892. Some recipients are now uncomfortable to remember - the society's early decades are inseparable from colonial expansion. In 2004 Harish Kapadia received the Patron's Medal for his Himalayan mountaineering, making him only the second Indian to do so after Nain Singh Rawat 128 years earlier. The medals continue. So does the conversation about what exploration meant and means.

In 2010 the society launched Hidden Journeys, a project that curates geography along popular flight paths - London to Johannesburg, Sydney to Singapore, Madrid to Rio. By 2013 the work had moved into the seatbacks: Singapore Airlines partnered with the project on its new Boeing 777-300ERs, delivering real-time geographical commentary to passengers as they crossed the world. As you flew over the English Channel, a pop-up appeared explaining what you were looking at. The society called it geo-entertainment. For an institution that began with men around a table debating where rivers ran and what lay beyond the next horizon, it was a quiet completion of the circle - the same kind of curiosity, now scaled to thirty thousand feet.