A breakable wall is a piece of structure that can be destroyed due to an action taken by the player, this generally being by striking it directly with a weapon. Once the wall is destroyed, a useful item will usually be uncovered for the player to collect (which in most games is a health-restoring item).
Breakable walls have appeared in almost every game that conform the Castlevania series, starting from the very first game, and have since become a staple in the franchise. As the series progressed and role playing elements were added to some of the games' mechanics (such as was the case of Symphony of the Night), not only walls, but ceilings and floors were also added to the roster of environmental pieces that could be destroyed. Furthermore, instead of simply revealing an item, they oftentimes give access to secret rooms full of treasures, or outright new areas of the castle.
In Castlevania II: Simon's Quest, breakable blocks can initially only be destroyed by tossing a vial of Holy Water at them (there's no breaking animation, they just disappear). Later on, they can also be destroyed by equipping the Nail relic and striking them with the whip. Some of them conceal special items and even clues. Furthermore, their contents can be revealed to the naked eye by equipping the Eyeball relic (in fact, they can actually be collected this way if the player is able to make contact with the item itself, without resorting to destroy any blocks). The ability of being able to see weak points on walls would later reappear as an ability obtained by equipping the Peeping Eye's soul, Search Eye, in later games.
Symphony of the Night introduced the concept of familiars being able to detect and interact (to some extent) with either breakable or movable walls. While summoned, the Faerie Familiar is capable of detecting a weak spot on a wall, fly toward it and tell Alucard out loud there's something odd about it. The Devil Familiar, on the other hand, is capable of noticing switches in the environment that are far away from Alucard's reach and press them for him, which results in a nearby wall moving out of the way and allowing access to new areas (a similar occurrence would be seen later in Castlevania: Curse of Darkness with the Proboscis Fairy).
While some games lack the presence of breakable walls entirely, these were instead replaced with mechanical barriers that required specific actions taken by the player to make them move out of the way (such as stepping on a pressure plate, interacting with or utilizing a key in a contraption, detonating a bomb, equipping a special item, or destroying an object to make a wall move elsewhere) and allow access to whatever secrets they hid behind them.
Two special kinds of walls were introduced in Castlevania: The Dracula X Chronicles, one made of Red Skeletons' bones and the other made of crystals. These would reform themselves immediately after being struck, thus impeding further progress, and could only be permanently destroyed by the acquisition of special items given to the player by two of the missing villagers after rescuing them.
Games with role-playing elements often include special items or means to identify which walls can be destroyed; either it is a familiar (usually a fairy or a demon) that can point out weak spots on the environment or press switches out of the player's reach, or accessories that can be equipped and which will react whenever the player is near a breakable spot (such as the Secret Candle in Vampire Killer, the Eyeball in Simon's Quest, or the Search Eye ability in some of the later titles).
- In classic titles, destroying a wall would usually reveal a Meat item. In time, this type of food item became to humorously be known among the gaming community as "Wall Chicken", with the term becoming so popular that it's now part of gaming culture worldwide and being frequently referenced among diverse forms of entertainment media. Part of the humor comes from the fact that:
- It would be absurd that someone would store food inside of a building's structure or that it was used as a construction material.
- It could remain in an edible state after a long period of time.
- Even if this was the case, it would be all dirty and not advisable to be consumed in that state.
- In the game Dust: An Elysian Tail, there's a health-recovering item called "Mysterious Wall Chicken", which as its name implies, is obtained by breaking certain walls in a nod to how similar items are often found in the Castlevania series hidden behind breakable walls.