Generally they can design a temple, castle, or other public structure that grants bonuses to everyone in the settlement. A specialty of the Imperium.
For some sample functions...
- Fortification (Greatness, Minimum Skill 9): Your defenders are greatly aided by the numerous defensive and offensive features of your architecture, gaining all the benefits of two Positive Levels (Eclipse, page 86) while they’re there or in the immediate vicinity. The effects can never be changed once selected, hence this is actually hundreds of different abilities. It’s also a very good choice, which is why it’s first, instead of being in alphabetical order like the other choices.
- Axis Mundi (Freedom, Minimum Skill 15): Defenders affected by unwanted spells are automatically affected by a Break Enchantment effect at the owners level once per unwanted effect.
- Every Advantage (Excellence, Minimum Skill 12): Your architecture encourages teamwork and specific tactics. Your defenders gain +4 (Morale) Bonuses to their Attacks, Damage, Saves, and AC. (Another ability with many, MANY, variations available).
- Glorious Bells (Serenity, Minimum Skill 18): When these bells ring (up to twice per week), every defender gains the equivalent of a nights rest – eliminating fatigue, regaining hit points, attribute points, uses-per-day powers, and so on, in an instant.
- [12:35 AM] Thoth_Manjet: Harmonious Layout (Amplify, Minimum Skill 9): All spellcasters on your side gain a +4 bonus on their effective caster level while in your stronghold. This doesn’t give them more spells, but it may upgrade their effects.
- Horns of War (Emotional Auras, Minimum Skill 12): When sounded (up to once per hour) these horns produce a Terror effect on all enemies in and about the stronghold.
- Runes of Despair (Emotion, Minimum Skill 3): Attackers suffer a penalty of (-12) on attacks, damage, and saves against mind-affecting powers – although they do get a save.
- Warded (Block, Minimum Skill 3): Your stronghold is virtually impervious to magic designed to change or damage it, including Rock to Mud, Move Earth, Passwall, Disintegrate, and so on.
Usually they can only add one function, experts can add two.