A Lightning trap is a type of Dirtamancy Trap that harnesses the natural Shockamancy generated in Rain and Storm hexes and hurls it at enemy units from the city's Tower. The first known such trap was installed in the city of Weatherbug by Dirtamancer Digdoug Mole.
The trap requires a cross braced spire of wrought iron (a lightning rod) be added on top of the city's tower, and modified or expanded spell storage. The harnessed lightning isn't stored as juice or spells, but used immediately against enemy units present in the city. The trap also gives the tower the ability to Automagically target enemy units both on the ground and in the Airspace, without needing a Caster or Warlord to order it so. This ability is so robust that when the city of Weatherbug had every speaking and thinking defender croaked the trap continued to fire, and would have continued to fire until a lone hidden Golem was croaked and the city claimed.
Normally these traps are only useful when a city is naturally prone to having rainy or stormy weather, otherwise the trap never charges. However, Carnymancy can allow a Dirtamancer to ignore Hex restrictions on traps and modify the trap to be charged from nearby rain or storm hexes. This was the case in the City of Homekey, which is near a rain hex and had a Lightning trap built in this way.