Unlike previous Stronghold games, the castles of Stronghold Kingdoms are separate from the village proper, and presumably are located just outside of the village; there is a path leading from the Keep to off of the screen.
The village will suffer a Popularity detriment if at any time the castle is not fully enclosed.
Players are given a 52x52 grid in which to place walls and buildings to improve the security of the castle. These structures are of three ingame types: Wood, Stone, and Buildings.
All players begin the game able to place basic Wood structures: the Wooden Gatehouse and the Wooden Wall. Wooden Platforms followed by all Stone structures are researched via Fortification; Buildings are researched with Defences.
In addition, the center of the castle houses an unmovable, indestructible Keep that provides arrow fire. It can be upgraded with Castellation, improving its firing rate. No structure can be placed in contact with the Keep, but troops can be placed around and within it.
Unlike village structures, the time to build castle elements does not take more time as more are built, and castle construction can be queued without limit; however, build time can add up very quickly. Build time can be reduced by up to 60% by researching Construction after acquiring Rank 5 Castellation.
Players may not fully enclose their castle without the use of Gatehouses.
Wood structures are built quickly, but fall easily to attacking forces.
- Wooden Wall - 1x1, available at start (Rank 1 Fortification), 3min 45sec each
- Wooden Gatehouse - 3x3, available at start (Rank 1 Fortification, 1 hour each
- Wooden Platform - 2x2, can hold Archers, Rank 2 Fortification, 3 hours each
Stone structures are far more durable than wood structures, and no stone tower is affected by enemy attack other than Catapult (or Captain's Catapult Voiley).
- Stone Wall - 1x1, Rank 3 Fortification, 15min each.
- Lookout Tower - 2x2, holds Archers, Rank 4 Fortification, 4 hours each
- Small Tower - 3x3, holds Archers, Rank 5 Fortification, 8 hours each
- Stone Gatehouse - 3x3, Rank 6 Fortification, 2 hours each
- Large Tower - 4x4, holds Archers, Rank 7 Fortification
- Great Tower - 5x5, holds Archers, Rank 8 Fortification
- Guard House - 3x3, +10 Castle Troop Capacity, Rank 1 Defences, 3 hours each. Very fragile until upgraded at Rank 4 (Wood), Rank 8 (Stone), and Rank 10 (Iron). Can only place 38 per castle for a total of 400 castle troops, including the 20 from the Keep.
- Killing Pit - 1x1, damages enemy (and only enemy) troops that pass over it, Rank 2 Defences
- Smelter - 4x4, allows 5 oil pots per smelter, Rank 5 Defences
- Moat - 1x1, stops enemy movement until dug up, Rank 7 Defences. The number that can be purchased is limited.
- Ballista - 3x3, provides automatic (unmanned) long-range, 1-kill-per-shot, but fairly slow fire. Can place up to 10 per castle, depending on the Parish's Ballista Makers level.
- Turret - 2x2, provides automatic arrow fire at the same rate as the Keep. Can place up to 10 per castle, depending on the Parish's Turret Maker level.
- Tunnel - 1x1, allows up to 50 defending peasants to emerge from a point that must be outside the white (normal build) line. The number is 5 times the Parish's Tunnelor level.
Stronghold Kingdoms does not allow players to directly control units during castle attacks.
When an Army reaches a Village or capital, the battle will resolve instantly, without the delay characteristic of playback. The player owning the village, as well as the owner of the army, if any, will receive reports containing a buttoin that initiates a visual playback of the battle that took place as well as the list of casualties and the Honour reward or penalty. There is a bug so that the playback may not resolve in exactly the same way as the original (unseen) combat and may end with a report that is different from the report from which it began, but the game proceeds from the initial report.
For Mountain Peaks and Highlands villages attacker access to parts of the castle perimeter is blocked with "rocks" rendering the castle more easily defensible. Other than castle elements, there is no other terrain or terrain effects.