Get your DEM Terrain data from here:

For UK there is higher resolution material available on UKTS (download - Railworks - Misc - Landscaping)

Place the .hgt files into this directory: ...\Program Files\Steam\steamapps\common\railworks\DEM\SRTM\

Note that the RW Blueprint Editor has the coordinates wrong, if you look them up on any map they will usually read like this:

Longitude: 57.43124
Latitude: -2.29352

But in Railworks, it needs to be the other way around:


also see: