More than terrain in the territory

Fantasy lore often has reference to magical ley lines, shifting rivers of hidden energy. Knowing where these ley lines are, especially where they cross or join, is of strategic import.

Yet how many games include effects from ley lines in the actual game play? I don't mean simply in the lore itself, providing colour to NPC chatter or at most serving as an excuse for a quest or two. The closest I've seen in WoW is in Netherstorm, where you can stumble into patches of invisible free flowing mana which replenish you - it's a pity these don't exist in the Eye of the Storm battleground though, that could shake things up in interesting ways.

Imagine a game world where the ley lines start out as unknown, where building your guild fortress on a ley line provides benefits equivalent to building on tactically advantageous terrain, where different ley lines are associated with different forms of magic (shadow, nature, demonic, spirit, fire, etc) which buff or debuff your spell casting. To make it even more of a game these ley lines shouldn't be blindingly obvious to passerbys, not even in their effects (adjust the random numbers, don't apply a buff). Let players wonder why they seem to get more crits in one place than another, watch the stats junkies pile on saying it's just superstitious interpretation of blind luck.

Later on, introduce quests or capabilities to map these ley lines. The full extent of these ley lines would remain incomplete because they occasionally flow through inhospitable territory. The capability for the mapping of a ley line could be dependent on the type of ley line, and the capability limited to those classes that can use that type of magic. Holy ley lines would remain a mystery to warlocks, demonic leylines a mystery to crusaders.

Later still, let players discover for themselves that these ley lines move about - gradual shifts usually, sometimes sudden re-wiring jumps. Be prepared for the whining from the early adventurers that built their power base on a nexus which has shifted. Introduce some means, expensive grand projects like cathedrals, where the flow of these ley lines can be influenced. The flow could influence not just their path across the map, but also in their strength - let there be wars of strategic interference, damming the flows to cut off the enemy further down the flow, etc.

As much as maps are not the territory, neither is physical terrain the final story.