From Introduction: Travelling underground has many benefits that above ground may not. It’s less populated, it (usually) has a entrance and an exit, and can bypass a lot of dangerous areas in the right circumstances. It does, however, also come with its risks. As a GM, you may come across situations where your players may want to avoid conflict by travelling across vast areas underground. Depending on the location, it may also be the only way players can travel to to get from point A to point B. Travelling underground can mean many different things: navigating natural caves, crawling through storm drains and sewers, or walking along subway rails.