Here's a project I worked on over most of 2024, to finish in time for the holidays. For those unfamiliar with N scale model railroading, the tracks are 9mm apart and the box cars in the picture you'll see are 2cm tall.
The glow is created using a mix of side glow and 0.25mm end glow fibre optic. Drilling hundreds of holes and threading them was incredibly time consuming, but weirdly satisfying when you get to the point of having bundles of fibre optic ready for the LEDs.