The resistivity structure of the Rybachiy Peninsula (Murmansk region) was studied in winter by audio-frequency magnetotelluric (AMT) surveys using long non-grounded lines and a preamplifier with a high input resistance. The acquired data were processed by robust techniques. Reliable measurements were provided in an audio-frequency range of 7–8 to hundreds of hertz. The results collected in winter with non-grounded lines were no worse than summer measurements with grounded lines. The AMT surveys can resolve the basement top under 5–6 km of low-conductive sediments. The obtained resistivity section of the area represents the transition between the Fennoscandian shield and the Barents shelf and comprises highly permeable water-saturated conductors. The basement depth estimate by inversion of AMT curves was proven valid by subsequent drilling. The AMT surveys have provided updates for the local crust structure inferred from seismic data. The method is applicable to surveys in the Arctic areas of Russia and other permafrost territories.