The Grail is an item similar to an artifact in the sense that heroes can carry it and exchange it between them in the same way as artifacts. In fact, the Grail is sometimes unofficially referred as the ultimate artifact. The Grail is typically hidden somewhere in the ground of Adventure Map, and finding it requires digging it with a hero. Recovering the Grail artifact and taking it to any town enables player to build town specific Grail Building listed below:
- Castle has Colossus
- Rampart has Spirit Guardian
- Tower has Skyship
- Inferno has Deity of Fire
- Necropolis has Soul Prison
- Dungeon has Guardian of Earth
- Stronghold has Warlords' Monument
- Fortress has Carnivorous Plant
- Conflux has Aurora Borealis (in Armageddon's Blade and Shadow of Death expansions).
The primary bonuses of Grail Building for all towns is extra 5000 gold generation per day and 50% additional creature growth per week. Additionally, every town has its own unique bonuses which are presented in their own pages.
If the map has no obelisks, it is completely impossible to find the grail (even if every single block on the map is dug on). Also, using "nwcoracle", a cheat that reveals the puzzle map, will have no effect and the puzzle will not show anything.
Finding the Grail
In order to recover the Grail, a hero must dig it out of the ground. Only one Grail may be hidden in the Adventure Map. However, it is also possible for a mapmaker to set any number of heroes and towns to carry the Grail in their backpack or have their Grail structure built, respectively. When the Grail is buried into the ground, clues to its location can be found at obelisks. Every obelisk heroes visit reveals a part of the Puzzle Map, which shows the location of the Grail marked with X. Typically the X becomes visible when when the entire Puzzle Map is revealed, but occasionally it will be showed before the last obelisks is visited. However, it is often possible to guess roughly the area where the Grail might lie, and systematically start digging it. In fact, the AI at hard difficulty levels start digging the Grail even if only a third of the Puzzle Map is completed.
When the Grail is taken to a town and the visiting hero with the Grail "visits" the Town Hall, a town specific Grail Building will be built. Noteworthy fact is, that the town can build the Grail Building even if the player has already built in that town, but after the Grail Building is built the player cannot built in the town that turn.
Appearance of Colossus is a huge golden statue of a soldier holding a sword and a shield. It increases the morale of all of the owner's heroes by +2. Although the documentation states that it increases all allied heroes morale, this appears to be wrong.
Rampart's Spirit Guardian
Appearance of Spirit Guardian is a totem pole with a winged horse on top. It increases owners all heroes' luck by +2. Although the documentation states that it increases all allied heroes luck, this appears to be wrong.
Appearance of Tower's Skyship "gnome-made zeppelin". It reveals the entire map for the player who owns it, and increases knowledge skill of the hero defending against a siege by +15. Revealed map is a permanent effect and is not cancelled if the player loses the town with the Skyship. Unlike the Lookout Tower, the Skyship can not be used to disperse the darkness generated by a Cover of Darkness. Having this building gives massive tactical advantage, and any player will be pefectly able to spot any attemp of siege or attack not only to this town but to all friendly heroes and buildings.
Inferno's Deity of Fire
Appearance of Deity of Fire is a enormous glowing devil that stands in the horizon. It causes every week to be The Week of Imp, which means that the population of Imps and/or Familiars are increased by +15 in addition to normal growth. External dwellings are not affected by this special week.
The problem with Inferno's Deity of Fire is that typically grail buildings are built long after the imps, a low tier creatures, are useful. In fact, it is Necropolis who benefits more from extra imps available to be harvested as skeletons or transformed into one.
Necropolis' Soul Prison
Appearance of Soul Prison resembles an obelisk with an upside-down pyramid halo on the tip. It increases the Necromancy skill of all the owners' heroes by 20%. Although the documentation states that it increases all allied heroes Necromancy skill, this appears to be wrong.
Dungeon's Guardian of Earth
Appearance of Guardian of Earth resembles giant skeletal humanoid embedded into the rock watching over the whole city. It increases power skill of the hero defending against a siege by +12.
Stronghold's Warlords' Monument
Increases the Attack of a garrison hero by 20 when defending against a siege. This bonus gives an absurd damage bonus, able to increase the damage output of even the highest leveled creatures by about 50%, any hero holding a town with this building is nearly unbeatable except by an overwhelming army or an opposing hero with a very high level.
Fortress' Carnivorous Plant
- Increases the Attack and Defense of a garrison hero by 10 each when defending against a siege.
- This boost is considered to be the best in terms of siege defense, not only it makes all units tanky but also gives them a powerful damage steroid , this is particularly useful for the Fortress creatures, who have somewhat low stats (but extremely powerful and annoying abilities) and allows them to achieve a powerful combination of destruction, tankiness and annoyingness.
Conflux's Aurora Borealis
- Fills the town's Mage Guild (*regardless* of mage guild's level) with all unbanned spells. (Excluding Titan's Lightning Bolt)
- The best Grail building, any hero that enters the town learns all spells there are in the game. However, in games with lots of towns all the important spells may already be available even without Aurora Borealis.
Cove's Lodestar 
Makes any terrain native to Cove (movement without penalty, +1 to attack, defense and speed, see and ignore mines and see quicksand). Cove's siege remains on swamp.