Knackers

You cannot use Spades to transform terrain, regardless of whether you gained the Spades via an Action or a Cult Bonus. Instead, collect 1 Worker from the general supply for each Spade you get.

Ability: You must downgrade a Trading house or Temple on the game board into a Dwelling to transform terrain. Downgrading a Temple into a Dwelling and returning 1 Favor tile (no change in the Cult tracks) into the general supply to transform a terrain (regardless of whether the terrain is the Home terrain of another player or not) into Volcano directly or indirectly adjacent to the Downgraded Dwelling. Downgrading a Trading house into a Dwelling to transform a terrain that is not the Home terrain of another player. Downgrading Dwelling does not count as a Building Action; no VP or Power can be gained from it. You cannot transform Terrains unless you have at least 1 Dwelling on your faction board. 

Stronghold: From now on, the cost of upgrading a Dwelling to a Trading house is 1 Worker and 2 Coins, regardless of whether the Dwelling is directly adjacent to an opponent's Structure.