The Destroy Walls spell is the final spell given in Dungeon Keeper. It allows you to weaken and destroy enemy walls, allowing you to attack them easily. Its high price, position of being last researched and its massive research time ensures its use only once most Keepers are prepared.
You cannot break through an enemy Keeper’s Fortified Dungeon Walls just by digging. You can dig through normal earth but, if it is fortified, you need to cast the Destroy Walls spell. The spell merely weakens the walls to plain earth again at lower levels, but at maximum power can cut large squares of earth out of a previous well-fortified wall, leaving the victim very much wide open for attack (in direct contradiction to the manual, which states: 'The spell does not destroy walls, just gets rid of the fortifying stone blocks and returns them to mineable earth').
This spell is both incredibly expensive and time-consuming to research (taking 7.5 times as long as the already slow Armageddon!), so it may be a good idea to train your spellcasters a bit before researching this, or alternatively, keeping a pair of Flies handy to sacrifice.
To cast the spell, left-click on the spells icon and then select the square of fortified wall you want to destroy. The wall becomes plain earth and you can then tunnel through before you rival’s own Imps have time to fortify it again.
You can also use this spell along with Sight of Evil to make it much easier to spy on enemies, as therefore harrass them with Lightning Strikes and the like. Simply use Sight of Evil to locate your enemy, find an area that's not currently inhabited, destroy the wall into plain earth (powering up the spell to 12000 should do it) and drop an Imp there (slapping, concealing and boosting his speed him may be useful). Now possess said Imp and explore the enemy dungeon, trying to see as much as possible and avoiding getting him killed for as long as possible. Locating the enemy Lair is incredibly worthwhile, but will obviously be the last stop on your tour. Now you can see the enemy's dungeon, feel free to make his life a misery, killing his creatures with lightning, and using cave-ins to stop his creatures using certain rooms.
| ||Armageddon / Call to Arms / Cave-In / Chicken / Conceal Monster / Create Imp / Destroy Walls / Disease / Heal / Hold Audience / Lightning Strike / Must Obey / Possess Creature / Protect Monster / Sight of Evil / Speed Monster|
| ||Call to Arms / Chicken / Create Gold / Create Imp / Heal / Inferno / Possession / Sight of Evil / Summon Horny / Thunderbolt / Tremor / Turncoat|
| ||Assembly / Create Imp / Deception / Detection / Electric Shock / Enchant / Exorcism / Heal / Possession / Seismology|
| ||Time Bomb|