Here's an idea for a second game with less structure and planning involved, just to test out the new method of alternating control.
Faro is a great nation of people. It is ruled by an Emperess, whose power is balanced with the Council of Lords, and on a third side by the Council of Faiths. The nation has its issues-- foreign wars generate refugees, trade routes are threatened by piracy, barbarian uprisings in its remote reaches must occasionally be put down, and there is disparity between the wealthy few and the broader poor-- but overall, the nation is stable.
This was not always the case.
Once, the nation was the pinnacle of tyrrany. Much of the regency had achieved untouchable wealth and power by bartering with extra-planar powers, an arrangement that brought the former reign the power to amass great wealth and influence at the price of enslavement of the people, acts of depravity, and draconian rule that lasted This nation has always known that it is built on the ruins of that civilization, which ruled for hundreds of years-- its architecture, monoliths, and infrastructure remain today, grim reminders of what gathered the fuel upon which the current empire feeds.
Much remains below the surface- literally, and figuratively. Some opportunistic parties still petition for the right to study the tomes guarded by the Council of Faiths, mages and sorcerers still practice under license by the empire, and occasionally rumors emerge that remnants of the former empire are still being discovered deep underground or in the remote wilderness of the empire's reach.
You are among those brave souls who has made a career from these discoveries. Whether as a long-term retainer of an existing power or a freelancer, you are experienced with the strange, mad mechanations of the old empire-- massive complexes for defense, storage, and torture... vaults of hoarded goods and wealth... mining tunnels repurposed with mad vision... vainglorious tombs, galleries, and collections of unusual relics. And traps... lots of traps, which were an obsession of the old lords, who often staffed and tested their defenses in sadistic competition.
Many resources have been raided-- Faro's armies maintains a corps of delvers and engineers whose mission was to capture these resources, and who sealed off and protected ruins to prevent them being overrun by the deep-dwelling creatures that were drawn to them out of their geographic features or some remnants of evil power. The corps now is dedicated to preserving places of archeological interest and patrolling for the sake of security. It's a cushy job, but it involves long weeks away from home and long hours underground.
New discoveries are rare-- more elusive year-by-year. Officially, delving into old-world ruins is considered a criminal offense, punishable by jail-time and hefty fines. However, special licenses are granted based on expertise and political favors. They require approval by the Imperator and both councils, an insurance deposit, a hefty license fee, and actual expedition funding. Upon receipt of said license, all parties must sign a contract. In doing so, they agree to accept full liability of any damage they cause to public property (such as a subterranean collapse that breaks an aqueduct above-ground), forfeit all property to the city in event of their demise, release all liability in the event of injury or death, and relinquish 60% of their monetary profits-- 20% to each branch of government.
Despite these expenses, a new expedition sparks up almost every year. In fact, five years ago in a quest called the Hive Crawl of Mintevol, a company returned a derth of amazing artifacts and wealth... of six partners invested, four survived, as well as nine of the fifteen contracted workers. Each worker's stipend was enough to buy a home outright. Three partners retired to the south coast, set for life, while one reinvested her fortune into her own Reclaiming company.
What are your odds? Three of ten expeditions turn a major profit. Usually one in ten makes a bloody fortune. If you're caught gaming the system-- trying to escape with your wealth-- your sentence of twenty-year imprisonment includes forfeit of all possessions. Most contracts include a clause that, if anyone survives, the estate of each who died gets a cut of the profits. This discourages anyone getting shivved and left in the deep.
You have a map of an entry point. It's an old well in a new-growth forest that, at one point, must have been a field on an estate. The land once belonged to a countess' estate, the ruins of which were reclaimed repeatedly over the centuries. It is promising... in applying for the license, you managed to downplay the potential, which is based on a combination of folklore and written history. The Countess was a reputed libertine with a penchant for powerful lovers, amassing fortunes in taxes and trade, but bored with simple power. Her downfall reportedly was her intemperance-- she serviced the mad emperor, Draxis III, a Tiefling Sorcerer who personally led his cadre of mages to eradicate her palace, family, and grounds 1,300 years ago. Layers of ash ten feet thick compressed to a brittle, pyroclastic sheet so toxic with corrupt magic that none would set foot on the grounds for a hundred years.
Little has been reclaimed since then, but the ground is like a living thing and coughs up relics from time to time. Livestock is occasionally found missing from the surrounding farmland, and there is evidence of crude hunting technology. Civilized artifacts are increasingly common on the grounds (cut stone, metal buttons beads and arrowheads, preserved bones, remnants of clay and the like). This well may lead to something so deep it has been undiscovered. Most assuredly, however, there are resuorces for an entire ecosystem in such depths, and something may yet dwell there that will be unwelcoming.
3-4 PCs partners, each with one or more of the following:
Knowledge (languages, history, religion, arcana, local knowledge)
Rogue Skills (climbing,trap building/disarming, magic item identification/utilization)
Engineering (mining, construction/stability assessment)
I'd like to keep NPC involvement to a minimum... sure, it makes sense to have a crew of mercs go down there to help you out, but that gets messy for mechanics. Let's suspend disbelief and have just the PCs do any fighting, trapfinding, and the like, but NPCs do boring tasks like maintaining supply routes, mining found resources, or clearing blocked tunnels.