Description: The Collisional Orogeny in the Scandinavian Caledonides (COSC) scientific drilling project characterises the structure and orogenic processes involved in a major collisional mountain belt by multi-disciplinary geoscientific research. Located in western central Sweden, the project has drilled its second fully cored borehole COSC-2 in 2020. It extends the COSC composite geological section through the nappes of the Caledonian Lower Allochthon, the main décollement and the upper kilometre of basement rocks. COSC-2 targets include the characterisation of orogen-scale detachments, the impact of orogenesis on the basement below the detachment, and the Early Cambrian palaeoenvironment on the outer margin of palaeocontinent Baltica. This is complemented by research on heat flow, groundwater flow, and characterisation of the microbial community in the present hard rock environment of the relict mountain belt. COSC-2 successfully and within budget recovered a continuous drill core to 2276 m depth. The retrieved geological section is partially different from the expected geological section with respect to the depth to the main décollement and the expected rock types. The intensity of deformation in the rocks in the upper part of the drill core might impede the analysis of the Early Cambrian palaeoenvironment. However, the superb quality of the drill core and the borehole will facilitate research on the remaining targets and beyond. Although on-site science was reduced due to Covid-19 related restrictions, COSC-2 drilling was complemented by extensive downhole surveys. However, the geological description of the drill core and the sampling party were severely delayed, with the later being held about two years after drilling, concluding the operational phase of the project.