A tunnel profile through the rocks in the upper part of Svartöberget in the vicinity of the harbour of Luleå, Northern Sweden, is described. The predominant rock is an amphibolite richly penetrated by dikes of red granite and accompanying pegmatite. These dikes also cut sparsely occurring dikes of an older, greyish granite variety. The roof and the walls of the tunnel are now dressed by cement plaster and are no longer accessible to examination.