The Haven players recently cleaned out all the secrets I had in mind for Experimental Facility Tuv, so I can share it now! The Citadel House Adventurers first entered this dungeon on November 11th, Year 3. This visit was brought on at the invitation of the Nekolyns, who accompanied them into the first level of the bunker. On this delve, they found the hidden stair in the kitchen, giving them access to the residential floor. From there, they passed the first puzzle door to the statue room (after searching all the unlocked rooms) and figured out enough of the broken-in mutation wing to disable the crystal causing the blight above. With the Nekolyns satisfied, they decided to try to disable the lightning on the residential level, but were chased out by a facsimile they turned aggressive. Wounded, they went home.
The next time they returned (January 6th, Year 4), they stayed for over a week and received reinforcements. During the first week of this effort, they disabled the now aggressive facsimile, accessed some previously unopened living quarters, and contended with the mad Nekolyn Laetian who had been stranded here under the influence of the crystal, though he escaped. They spent the weekend recovering and awaiting reinforcements and resupply. When the others arrived, they solved puzzles and accessed the other two wings. In one they cleared a fungus infestation and disabled the lightning enchant, making ingress and egress much easier. In the other, they followed a long passage (the southeast one for over a mile) until they fought an extremely dangerous predator that used illusion to confound them. With some of them badly wounded, they withdrew back to Citadel.
It was over a year before they returned again, February 9th, Year 5, at the behest of the Nekolyns. In no rush, they searched the place from top to bottom and with the help of a living rock they found discovered even the most secret doors to the secret lab being used by an infiltrator to the facility back when it was functional. Loot was a significant haul. They also encountered the large facsimiles used to dig the tunnels. Wounded and tired, they awaited reinforcements.
When the new arrivals from the Vale, they followed the South tunnel as it spiraled down thousands of feet and it brought them into the underdark where they were repulsed by dangerous enemies. Now believing that all the tunnels lead to dangerous underground connections, they departed with little intention to return. The Nekolyns know that the South door is the most likely to contain continued danger and the facility has been turned over to them.
I’m considering starting a Patreon so I can make some of my prep available without it being player-facing. If you’d be interested in that, let me know so I can determine whether or not to put in the effort.