The Champaign Faire is no joke to construct. Even the first level of it's main building costs both Gold Florins and marble Slabs and the costs only get steeper with every additional level. However, the display of wealth is unmatched. This is the perfect district for a Rank 5 settlement rolling in cash and resources and ready to blow off a little steam. The Prosperity boost from your reveling population is significant, along with the Security penalty for creating opportunities to steal from drunk people.
Action - Work on Vineyard
There's always a few tended vines in the Champaign Faire. Players can choose to spend a hot but incredibly rewarding few hours picking either Grapes or Olives from the local Vineyards. They are joined by common laborers and ancient priests who look like they've been tending these vines since before the settlement was founded.
Main - Grand Pavilion
Every level of the Grand Pavilion is expensive, but highly rewarding. This building is the center of a 24 hour partying lifestyle. Here money is spent and days are lost to La Dolce Vida. Every Peer you set to live in the Champaign Faire will buy Wine for Florins from it. It also somehow increases Tax yield from all other districts in the Department of Commerce.
Exclusive - Trading Tent
Trading tents can only be built in the Champaign Faire. Everywhere else is too rough for them. These delightful almost-buildings cost Litra and Canvas to construct/upgrade and make money based on the actual player-fueled market trades. Each Trading Tent makes a small amount of Silver Thalers from all local Settlement Market Trades. They also store carts for their owners and provide a local Prosperity bonus (along with the usual Security penalty).
Linked - Vineyard
The finer aspects of society living are not possible without Vineyards. These valuable buildings are the only way to harvest Olives and Grapes, which are in turn the only ways to make Wine and Oil. (Technically, Fish can also be pressed into Oil, but Oil Presses can't be built without Olives.) While Vineyards can be built in any district, they grow their precious fruits best in the Champaign Faire.
Minister - Faire Commissioner
Whoever is hired to manage the Champaign Faire becomes the Faire Commissioner. They contribute bonuses to the district based on their Arithmetic, Management, Acumen, Influence, Grace, Philosophy, Mettle, Celerity and Might. This position, like most seats in the Department of Commerce, is best served by a Trader Lord. They are backed, unsurprisingly, by the Faire Commission ministry who handle wine deliveries and drunk wrangling.