Lateral Gallery 1 (GL1) in Cova del Gegant is a Middle Palaeolithic assemblage yielding diagnostic Neanderthal remains, together with Mousterian tools and faunal remains. It is a good archive for evaluating the environmental conditions of the coastal areas during MIS 4 and MIS 3 in the NE of the Iberian Peninsula, and also the Neanderthals’ behaviour and mobility. Here we provide a comprehensive assessment of all of the data available from GL1, such as lithics, human remains, fauna and chronostratigraphic details. The biotic ecofacts studied point to the development of a coastal plain in front of the cave and indicate that local conditions likely favoured a large variety of ecosystems characterised by open environments and woodland-edge taxa, and favoured repeated visits by humans during the Middle Palaeolithic. The evidence suggests that the gallery was mainly used by carnivores, such as hyenas, and also by Neanderthals as a brief stopping place, in view of the presence of transported and abandoned ergonomic lithic artifacts and/or the placement of bodies (or parts of bodies). The regional context suggests high human mobility and emphasises the variability of Neanderthal behaviour.