Asberget Tunnel I think? On Botnaibanan Railway or something like that. I couldn't find anything on the net, that showed it. I'll have to find it -- you've gotten me curious now. It wasn't so much the size of the tunnel, it was barely longer than one train, it was the fact that the tunnel went in, the tunnel looped and the train was headed 270 degrees off and an elevation of another 800 or so feet.
Add to that Millau Viaduct. and the Falkirk Wheel. I think I should have been a civil engineer or architect.
