Somebody else posted their tall bridge used to get the Glacier achievement, but I can’t find their thread at the moment, so please excuse my creating another one.
This is a medium world with flat terrain. My first attempt just went across the map but didn’t get high enough.
For attempt two, I took advantage of a few small hills along one side of the map to lower construction costs and thereby let me extend the line up longer before returning to earth.
(larger image here: http://www.designamatic.com/GraphicsTrainFever/TrainFever-GlacierLine03-Medium.jpg)
Didn’t even have to go all the way up to get the cheevie! 😉
Construction cost: 1.32 billion.