Since no one has posted a monthly challenge until now, I'll just post one. This month's theme is local railways and Interurbans.
This month's task is to build railways connecting suburban or rural communities to the rail network. Due to cost issues, these railways often have very simple infrastructure, they're often single-track, have tight corners, run on streets or are built to a narrower rail gauge or structure gauge. They are usually built for passenger service, even though a few of them have freight service. They are usually electrified using some low-voltage DC standard, such as 600 V DC.
Real World examples for local railways or interurbans include: * South Shore Line * Vienna local railway * Attersee Railway * Halle-Bad Dürrenberg Railway