I don't think anyone has mentioned the Quayside Branch, rermarkable for two reasons: first that it followed a semi-circular route mostly in a tunnel from the sidings alongside the main line to the quay below and down-stream of Tyne Bridge, and second, it was electrified by overherad "Tram wire" and operated by that "Crocodile" loco they have in the mueum at York. I have seen that loco coupled to an 060 steam tank engine double-head a train off the quayside and into the tunnel. On another occasion a train of wagons, brake van to the fore, ran away down the tunnel, into the shunting yard at the bottom, and the brake van climbed vertically up a warehouse wall by the force of the train behind it! I have the newspaper cutting photograph still!
IIRC it was powered by overheads in Trafalgar yard and along the Quayside, with 3rd rail in the tunnel - plenty of stories where someone forgot to lower the pan and it hit the tunnel front...
Part of the line is still in use for the Tyne and Wear Metro, it is part of Stoddart Street sidings which are used to turn sets in the early morning.