The inner membership of the Benevolent Grotto Society, controling and providing access, are a group of mid to low level Faerunic clerics, Harnic High Elves and Half Elves, children of Thalion Paurgiliath Arch Duke of Eltán who remained in Waterdeep after the The Free Imperia's Embassy was burnt by Vampires.
As of AR20 in the Free Imperial calendar, they are a solidly established long term minor faction in Waterdeep. They have excellent contacts and intelligence, and are trusted with the management of a Sanctuary which is valued highly by multiple powerful factions and entities. They have ready access to resources to facilitate the smooth operation of the Grotto.
They remain allied with Free Imperia interests, and provide regular briefings as well as other services.
Terrified, and many of them having lost friends and family, at first they hid in their respective temples. They began to realize that while the temples were devoted to good, they did very little to remove members who drifted towards evil. As this unease grew, they met in twos and threes and discussed the problem.
They needed sanctified ground that could be further fortified and powerful friends. Once this was achieved, they could try to use their abilities covertly against the vampires, but they had no hope if discovered or in a direct engagement.
Having no immediate ideas how to achieve these goals, they began a very abstract series of meta divinations about what courses of further divination might lead to the best results.
This led to records searches in church libraries for references to consecrated sites or rituals that would have required such. Crosschecking these against modern records was easier, but still time consuming. Throughout this process they used only the mildest divination to speed their research, based on the advice of a meta divination about how to proceed.
When they discovered records of Sharessian Revels in an always sunny crystal grotto of hot springs and pools amidst gardens, they could find nothing to steer them towards a probable location except that mentioned attendees seemed to mostly be from Waterdeep.
Trying to divine the location, or the name of the owner, was actively blocked - a blank, a negative data zone, notable for its absence. They realized that had they used divination in their record search, they could easily have gone right past the grotto's existence.
Trying to track people who had attended events a hundred and some years before was difficult, and at first exciting - but all the trails seemed to end at gathering points around the city. Guests must have teleported in.
It was during the depression caused by this dead end that
Ginnathiaras Paurgiliath - !Necrophant!(2) - !Velsharoon!
Was snatched from the Temple of magic by lich cultists. By the time the family discovered his plight, it was too late. He had been forcibly, and irreversibly, converted.
They didn't have the power for vengeance, but they had another grudge. And they needed a safe space soon.
Finally, through a yellowed personal journal, they found a reference to the long deceased author being invited to a Crystal Grotto revel by the owner of a festhall named the Cat's Meow. It was a thin thread, but trying to divine the location of the Cat's Meow brought a familiar blankness, which was in a negative way, encouraging.
After more days poring over historical property records, they discovered the original site of the Cat's Meow, lost to a fire in an appropriate time window. Records showed that it had been built over by a tailor's shop, then merged with a larger wheelwright next door into a factory for Sonky's Slip Ons (possibly a sort of raincoat?).
The factory had been caught up in urban beautification, and refit into townhouses and loft studios. There was a record of trees being planted. The building had changed hands regularly, showing that the value had climbed, peaked and fallen off long ago.
Proceeding to the site revealed that it was all but derilict, with a 50 year old white 'Sonky's' showing through on the fading painted-over brickwork. Many of the interior walls had been cleared out on the first floor, and an unlicensed eatery was doing brisk trade.
However, while a block away they could clearly detect the sewer with a dowsing rod, as they approached the building, they found their old friend: blankness. Not just a blocked sewer, but a completely unresponsive rod; suddenly just a forked stick.
An augury suggested that exploration through the border Ethereal would be safe, but to bring tools and plan on a bath after. When they finally stumbled into the grotto, some 50' down, they had to contort around decaying plant matter to find room to return to the Prime Material.
The more of it they cleared, the more excited they became. When they discovered the Grotesque Baroque framed mirror built into the wall, pumping in sunlight behind its curtain, they were ecstatic. And when they learned what the mirror was and did, they hardly minded the annoying ghost living in it.
Within a month, they had negotiated the charter of the Benevolent Grotto Society with the various churches, and written themselves into the core of it. The church of Sharess would host it as a Sanctuary for good and neutral interfaith clergy. Their own churches were delighted to assign them permanently to the project, getting in on the ground floor of a going concern
The Paurgiliaths bought the surface building for a song, employed the chef of the eatery (who turned out to be brilliant), and fixed it up as well, renting many of the rooms to followers of Sharess.
They have potentially hereditary positions as Gatekeepers, with the protected right to expand their number as they see fit. They can retire, but not be removed by the Church.
The Gatekeepers have guard rooms fronting extensive suites on either side of the Mirror's entry hall, easily housing 30, and with laboratory space, private kitchen and bath, and storage areas on each level.
They also have a permanent guest right to invite up to 30 more guests and put them up in apartments. They could pay to house extra guests like any member.
Thus, providing safe house facilities and agents for the Free Imperia or expats from Harn or Krynn is quite naturally included in their role. They could sweep visitors up from the Realmspace side of the Pyramid Gate, house them, drop them wherever, and return them as needed.
They have filed with the Peacekeepers as an allied auxiliary organization, but display no overt Free Imperia paraphernalia.
These priveledges came with corresponding duties. They pick up or drop off about a hundred revellers or other clergy a day. The grotto maintains an internal average population of perhaps 150 revelers, another 75 various clergy, 100 guests, and perhaps 10 of the original 15 Gatekeepers at any given time, with another dozen security. All these numbers, of course, swing widely.
They keep the mirror running with multiple operators and two safety crystal balls which don't broadcast a gate in three shifts around the clock.
When people aren't actively passing through the gate, or being hustled through to the party, the operators amass intelligence. This is where they hope to achieve an eventual revenge on the Vampires and Lich Cultists.
Now, while they aren't unknown, they are widely regarded as something between boring technicians and theater ushers, and their real objectives are unlikely to come to light. Further, they operate from a heavily protected position, further strengthened by the self interest of many powerful people and entities.
They gather a great deal of data. Intelligent people and spell users are the most likely to notice being scryed on. Wherever possible they avoid or limit that circumstance, because there are almost always people who don't fit that description who see the same things. The Mirror's ability to read minds they apply with a light touch.
First, they use the mirror and their role as Gatekeepers to quietly aquire minor but trustworthy allies. They know which City Watch Captains are mostly honest, and which one was replaced by a doppelganger.
They have a friend in Import Tax, who's only too thankful to come valuate a specially imported load of goods. A friend who rents stalls at the market, a friend who rents boats. Friends in adventuring companies who like working security at the Grotto.
Second, they use auguries and networking to guide the use of scrying with the mirror, and very carefully track signs of evil. People who have suffered from psychic attacks or evil magic are much less likely to notice being scried than the monsters responsible.
Bloodless corpses or plagues of rats naturally get mentioned at the City Watch's Wednesday service with the nice Holy Strategist.
And having a Paladin standing by so that they can detect evil and evil intent when viewing crowds has been awfully useful.
Even when no corpse is found, a missing person leaves a trail of thoughts bouncing through those who don't see them. And evil, the kind they are tracking, kills. Finding places with more missing people, tracking their lives back, gives a gradual but clear map of hunting zones.
Sometimes they even deploy a cleric through the mirror to cast 'past life' on a corpse and view its last hour of life, but they try to keep boots off the ground and leave no traces of their interest.
When the High Forest nature types are working with them, they can question animals, see through their eyes, or rummage gently through their bright memories.
The homeless and dispossessed often see more than others, when an area has been narrowed down. They are also less likely to react significantly to being scryed, even should they notice.
Once a lair of a monster or a predictable hunting pattern has been nailed down, the Gatekeepers do Divination to see who would make the most effective use of the information, and Auguries to find the most untraceable way to inform them. Then they drop a dime.
For various monsters and cults they have tipped off the City Watch, adventuring companies, Harpers, high level Paladins who would never go to Grotto parties, the werecats calling themselves the Eyes of the Evening, who do, once even one of the lords of Waterdeep, and not infrequently other villains who might weaken and expose both groups with competitive practices.
They haven't trapped Master Vampires, or brought down dark gods, but they do good work from a solid position.
The Gatekeepers of the Benevolent Grotto Society relay daily telepathic briefings on anything of interest to the The Free Imperia to the duty officer at the Great Imperial Pyramid gate.
When Free Imperia authorized personnel go back and forth they help with intelligence, safe houses, commercial agents, smooth teleport travel and insertion, security, etc.
As a Peacekeepers Registered Auxiliary, they get support in materiel or sklled personnel, but in return would cooperate fully to enable any Peacekeepers deployment to Realmspace.
Since the WATC has started exporting a little, they have been invaluable. As a well established Waterdeep institution, the process of taking the goods through blind trusts, getting them certified taxpaid, and out to traders and markets in the same day, without Arda or the Free Imperia beng mentioned has been well thought out and smoothly arranged.
They even installed a tiny boat, just big enough to have a cabin with a door, in the largest pool in the Grotto to aid in loading and unloading Holds of Holding.