My favourite railway oddity -
The Bishop's Castle Railway - was built with the intention of linking Hereford-Shrewsbury line to the Newtown-Oswestry line. Except it never made it ... they got as far as Lydham Heath, ran out of money, and so built the track back to Bishop's Castle so that at least it'd have somewhere to go to. They started work on the railway in 1865, went in to receivership in 1867, and remained in receivership for nearly 70 years until it was finally put out of it's misery. Was too much of a basketcase to be in a grouping. A company in Cammel Laird bought all the scrap metal from the railway after it was shut down and smelted it down to build a battleship (HMS Prince of Wales). That was built in 1939, and within 2 years had been sent to the bottom of the south china sea by the Japanese. All that remains of the railway is a couple of rivets from the last engine (the Carlisle), which were at the Bishops Castle Railway Museum (which is, unfortunately, closing it's doors very soon).
But anyway ... it was half-built. Does that count?