Castles are the main defensive structures in Happy Wars. Protecting each team's Big Tower, each castle is outfitted with defensive Bomb Rocks and 8 Ballistas. Players initially spawn in the castle.
Although most players may leave the castle immediately when the game starts, it is a huge advantage to have at least one cleric (equipped with the dispel skill to get rid of the pesky ladder materials) guarding the castle at all times.
It's always in good practice to have Engineers defend and build Gatling Guns to defend the castle. Try to have Dispel+ on your weapon, as it will come in useful when enemies are coming to build. Engineers can also repair the castle gate.
Destroy any cannons or missle launchers in front of the castle, as enemy players may use it to their advantage and destroy your castle gate within only a few seconds.
Sometimes, a well-placed castle rush can cost the match for the attackers. When you are on the ropes, rush their castle. Some bots will spawn at the castle (and also a couple of players), which (assuming your defenders are well-trained) can push away the siege, or win you the match.
If you are an Engineer, try to repair the gate using the Repair+ skill. 1 minute of constant repair can make the gates HP restore by at least 25% or more depending on what AP buffs you have.
On a full-scale siege, allocate your resources accordingly. Always have a few good Mages to take out the enemy's anti-siege gear and a set of good Clerics to support allies and summon materials. Warriors should be used sparingly and ALWAYS be taking out the enemy's resistance.
On a solo stealth strategy, never go for the gate. Always rush as a Cleric (or wait for one of your allies to spawn as one). Build the ladders. If you attack the gate for at least one moment, the enemy will be alerted to your presence and may catch you off guard.
Having Anti-material as a buff is a good idea as you do more damage to things such as gates, turrets and other destroyable builds.
Warriors with Charged Attack can destroy the Ballista/Gatling Guns on the castle from the outside. This is done by charging the skill until it is at a stage 5 attack. It also has to be done on the side of the platform it is on or else you will hit the platform instead. This can also be done with the Ballistae on the top of the castle (above the gate), however, this requires players to be just slightly away from the front of the castle.
The Spinning Blade skill does the most damage to the gate it is recommend that you that get your spin to level 3 and have conserve AP buffs.
Have a mage activate the Lightning Arrows team skill directly in front of the castle gate. The lightning arrows do more damage to structured buildings than players. This can be better than an alternate to the battering ram if enough people are involved.
Mages are invaluable for sieges on Castles; their wide array of skills help take down the structures and enemy players around the castle.
Bots are prone to either stay back at the castle to guard, or teleport back when players get near it, so don't lower your guard!
Bots tend to release the Bomb Rocks on the castle even if there are no enemies.
It can be speculated that the castle walls themselves have an indoor area as windows are seen around it. However, the walls themselves lack doors so it is unknown if the area inside the walls are used.
During the holiday season the castles change appearance to match the holidays (this in no way affects gameplay).