Charles Darwin visited Galápagos for five weeks, from 15 September to 20 October, in 1835. This is a small fraction of the total of 248 weeks he spent on the voyage of the HMS Beagle (27 December 1831 to 2 October 1836), yet his experiences in Galápagos were of disproportionate importance in the development of his scientific thinking. As he wrote in his autobiography, he was deeply influenced by his discovery of the similarity of Galápagos plants and animals to those on mainland South America, and especially ‘by the manner in which they differ slightly on each island in the group’. But while in Galápagos, Darwin was primarily a geologist. He repeatedly attempted to explain the geomorphology he observed in terms of processes he could only infer: uplift, the direction of lava flows, their terrestrial or subaqueous origin and the eroding effects of seas. He also developed a theory of magmatic differentiation from looking at crystals embedded in the volcanic rock. Where was Darwin in Galápagos and what did he see? Much has been written about him on his visit to the islands, but there is still confusion about exactly where Darwin set foot upon the four islands he visited: Chatham (San Cristóbal), Charles (Floreana), Albemarle (Isabela) and James (Santiago). Only one study has attempted to elucidate his whereabouts, but it lacked information from the most revealing manuscripts and so was incomplete and incorrect on points of detail. We attempted to answer these questions by first conducting an extensive search in bibliographic material for relevant information, and then by retracing his steps as best as we could from 19 October to 14 December 1996, that is at approximately the same time of year and season (dry) as Darwin's visit. Here we describe the route he took, several of his key geological observations, and changes that have taken place to the fauna and flora since his visit 165 years ago. By visiting the places he visited we were able to appreciate what caught Darwin's attention, and why. The geological features seen and noted by Darwin are still extant today. The living world is in sad contrast, for it is no longer possible to see several components of the fauna and flora he observed. Thus the information presented here is of potential value to scholars wishing to revisit his sites for historical or for scientific purposes (figure 1; see table 1 for GPS readings).