From Wikipedia: The Thamshavn Line (Norwegian: Thamshavnbanen) was Norway's first electric railway, running from 1908 to 1974 in what is now Trøndelag county. Today it is operated as a heritage railway and is the world's oldest railway running on its original alternating current electrification scheme

Boarding times, maps, more info etc: https://oi.no/besok/thamshavnbanen