The Ley Lines

Throughout the world, these are metaphysical currents, also known as the Dragon Veins, running above and below the surface of Taeingarnor that, like veins in a body, pumps the blood, Mana, across the globe. Mana is a form of energy that never stands still on its own, causing it to flow, reportedly, like global rivers. These rivers supply arcanists with the energy that they utilize for their casting of spells and rituals and artificers with the energy that they utilize for their majitek.
The Underworld, with its innumerable tunnels and chambers, is frequently passed through by the Ley Lines, but given the size and number of them, the areas with civilization in the below that are lucky enough to experience this phenomenon are few and far between. Even fewer are the areas with readily available tools, magic and personnel that can harvest and utilize this rare occurrence before it moves.