The latest Monday Mashup, number 43, is something I have ridden many, many, many times.
The New York City Subway System
The NYC Subway was for me in NY, the way I got from place to place. It was the means by which I travelled from the Battery to the Cloisters, from Times Square to JFK and Shea Stadium.
I’ve had dreams of the subway, dreams of subways of alternate New York Cities, even. And there is the fodder for my mashup.
I’d probably use a system like GURPS, borrowing from their Time Travel book for it. Set the characters in New York, taking the subway to some destination. When they get to the stop and see that its the “Royal Museum of Natural History”, what will they do? And if they continue to work through the subway, they will get further and further from their home reality, until they start to work with the map of the Subway and begin to figure out the patterns inherent.
And just what do you do now that you’ve found an interdimensional subway system, anyhow? I can see a lot of campaign fodder out of the idea.