Four ideas: Rumors, Bastions, Training Camp and Vanguards.
Rumors: simply add a "did you know?" line to the Inn's interface, that changes every time you select a Inn... something to add flavour and/or to let new players know some of the aspects of the game, like "A shield won't do any good to thee against a good Crossbow", or "Some peasants say that fish in the rivers can be eaten... amazing", or "stone is heavier than arrows, let's take some to a tower and throw it at the enemy!".
Bastions: harmless units with no attack, that die in 1 hit from any melee unit, but are nigh invulnerable to arrows, resistant to bolts, can take up to three stones from a tower before being killed and will intercept (and be hit by) any arrow/bolt/stone (fired by the enemy) that happens to be traveling through the same square the Bastion is in (only those fired against people: buildings are too tall to be protected this way).
Their special equipment could be produced in the Siege Workshop and operated by somebody (a Recruit that goes there when the equipment is ready, akin to a newly built Tower? Another specialized citizen?).
Training camp: a building (maybe the Town Hall's recycled sprite?) where unused specialized citizens (everybody except serfs, laborers, and recruits) go instead of idling around.
When there, they can be selected similarly to the wares in the Market and can be trained to become Recruits.
Also, instead of a civilian you can select food: if you do, the Training Camp trains Recruits from Food (better: trains them instead of hiring them with Gold like the School does); it takes longer than hiring them in the School and you also have to wait for some Food to be delivered (similarly to how the Market works), thus if you have the Gold and Coal to spare it's still better to just hire them.
Of course, the Food cost should be lower than the corresponding cost of Gold in the Market...
(I know, I know, I shouldn't be recycling older ideas

)
Vanguards: harmless units that can be controlled like soldiers but are extremely frail, have no attack, can be hired at the School and can be ordered around during Peacetime.
In order to limit them to the exploration of your Town's surroundings, their Hunger bar drains very fast whenever they move.
A button where normally the Storm Attack button is located lets the player convert them into Serfs with the same Hunger level.
What do you think?
Just when you think you know something, you have to look at it in another way, even though it may seem silly or wrong. You must try! - John Keating, "Dead Poets Society"