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After the party's research, they should have discovered that Viperwall is a Serpentfolk stronghold on the north-east of Ember Lake. The lake is apt to be foggy in colder weather, since it is fed by hot springs as well as several rivers. Swimming in the lake's depths are charig - diminutive phosphorescent lizards like salamanders, which are responsible for the lake's name.
The stronghold is carved from the cliff face, quite a large edifice with many arrow slits, small odd shaped windows, and innumerable strange carvings. Around 400 yards off shore is an oblong rocky island, maybe 180' x 120'. It is a jumbled hump of rock, but most notably for the numerous ~30' tall carved stone columns that adorn it. The columns appear to have been built to roughly resemble tall-standing snakes , but not much effort has been put into realism. The effect might seem amateurish, but ends up being quite eerie instead.
During the day, the island is occupied by around two dozen people. Nearly all are muscular human males (many are shoanti tribesmen) although, there are two half-elves (one female), a dwarf, and two human women. Although they are guarded by two serpent folk (one normal, one large), they aren't restrained in any way, and seem to go about their task of building more columns reasonably cheerfully. If they notice the party approach, the notify the serpentfolk, who direct the workers to the side of the island away from the party.
The serpentfolk will wait for the party to come ashore, and then ask them to leave, and allow the workers to continue their "holy work". They have little patience for intruders, and will soon attack if the party doesn't leave. The smaller has a blowgun (1d2+poison dmg, 20 range), and the large one has a mattock and 7 javelins. He is large sized, so AC and to-hit lower by 1, he has 10' reach, mattock dmg 2d6+7/x4, javelin dmg 1d8/x2). The larger one is wearing a set of muleback cords, which are useful as he carries rock around the island.
One of the slaves working on the island is James Rookweather, who the party has been searching for. He, and all the other slaves are under daily suggestion that they will be free to go once they finish their appointed task. That their tasks never seem to end is blotted out by the magical compulsion. He is friendly, and willing to take a break from work to discuss things. He has discovered that his friend Marciano Mayfield? is working to help decorate a temple of Gozreh on the top level of the compound. Unlike the rest of the compound, the temple is easy to access, and the dorm for the workers is currently adjacent to the temple.
The gates to Viperwall are opened rarely, and the guards are intelligent and wouldn't likely open the gates to strangers. Opening the gate would require a DC 35 disable device check, and sneaking through the passageways at night would require two stealth checks - one for a normal serpentfolk, and one large one. If a combat lasted long at all, much attention would be attracted, and the serpentfolk would try to acquire new slaves.
