A hundred and some years ago the banks of the Hudson River were considered a development resource. There were many mines along the river, and railroads run up both sides. There are still a number of active mines.
Back around 1890 they were going to turn Dunderberg Mountain into a ten mile long roller-coaster. It was going to have two uphill grades, one going due north and the other west, connected by a short 270 degree downhill loop. Dunderberg is mostly one big rock, so they were going a lot of blasting and construction with the remains of the blasting. They built two construction roads up the mountain.
The eventual plans were to build a resort and probably casino at the bottom, and a restaurant and hotel up at the top. The reverse direction was a bit steep, but within the capability of a steam engine, so they were going to supply the restaurant and hotel via nightly railroad deliveries.
The views are just incredible. On a very clear day from the top you can see New York City. Even on a misty day you can see a vast stretch of the Hudson River. Right now, you get a great view of the Indian Point nuclear power station, but of course that's recent relative to 1890.
So they put the equivalent of $24 million in 2014 dollars into this construction, and .... they walked away from it, about 60% constructed. Some of it, they had done nothing. Other parts were ready for ties and rails. They built each section separately, so there is no long stretch of finished railbed. No doubt they planned to lay the tracks in reverse order, with the train backing up the downhill grade, delivering ties and rails as it went.
This picture is taken from NY-9W south of West Point. You get a great view of the second loop, which is the only loop which would get a rider an expansive view to the north. The snow highlights the railroad. Towards the right hand side, it's harder to see. It's not obscured. Instead, it's simply partially built there.