Often hidden by grass, other vegetation and sometimes shifted earth is a series of metallic rails that connect the major landmarks of the valley. The rails are made of the nontarnishable, nearly unbreakable Slith silversteel and consists of a single 1' wide and 2' tall strip that seem perfectly formed. Once found they make finding new locations a breeze if followed but they come with several potential dangers.
Another danger is that once powered the rails will begin drawing out mechanites who want to feed on the energy. If no one gets too close it might be amusing to watch them approach the rail, get stuck on it and then get sent flying off. But they'll keep coming like bugs to a light and many will be destroyed likewise.
The final danger will come when the residents of the Rail Station discover how to use the railcars and begin travelling...
Note that at each location in the valley will be a rail stop - at this point all that remains are some silversteel girders that used to hold together more ornamental and less durable material. Random bits of Slith stuff may be uncovered in these spots if investigated.
The most immediate threat in the valley is based out of the Rail Station. When the Slith disappeared most of their servants went on to try and reform a new civilization as independent beings. The servants in this valley were so isolated and remote that they never got to take part in that. When the power shut off and the valley went quiet they slowly descended into desperate savagery. They did survive, though, a motley assortment of different races gathered, modified or created by the Slith. Ages worth of unlikely crossbreeding, inbreeding and other accidental acts of miscegenation took place and now the residents are simply the Twisted.
The Twisted appearance is almost random with different traits of elf, dwarf, human, goblin, orc and beast randomly assorted among them. They have never taken up metal crafting after all this time but rather make use of the scraps of silversteel that they find everywhere. However their priests, whom someone is answering, have a ritual that lets them shape silversteel. This is reserved for the most important of the Twisted. The majority of the Twisted wear poorly maintained sackcloth clothing and use wood and stone tools with the occasional improvised silverteel implement.
Their language is a simplified, degenerate version of the Slith tongue. However it is close enough that if pressed a member of the Twisted could read Slith writing (though not necessarily understand what the words mean). These misunderstood words make up the nonsense rituals of their priests who hold the Slith as distant gods who will one day return. In the meantime they claim to be guided by "The Buzzing", a buzzing voice that only the select can hear in their heads. The Buzzing currently seems to be guiding them to dig into the mountainside, ostensibly to teach them how to make their own silversteel...
The Buzzing is also incredibly xenophobic in how it will react to outsiders. Individual Twisted may initially be curious or friendly, perhaps even mistaking the PCs for the returning Slith if they have better than primitive technology.
The Rail Station
With the ageless silversteel acting as girders, the Twisted have managed to keep the basic form of the Rail Station even if most of the original ornamental stone walls have crumbled to the ground. Simple stone walls sit between girders and leather hides cover where most of the arched roof has fallen down. The station is massive, about the size of Grand Central Station, and is filled with individual Twisted huts and tents with the leaders and shamans taking the individual private rooms.
If the Rail Station is looted, generally useless bits of silversteel are all that they will find in the common tents. The private rooms are where the shaped silversteel blades and armor can be found - assuming they aren't being worn by the owners. Other random bits of Slith debris are also possible. There are also stairways down to the underground.
The rail lines actually run into an underground portion of the Rail Station. The tunnels that the rails follow down are blocked by large silversteel doors that will open once the power is turned on. They all meet in a large switching station where there are still five intact rail cars - long, art-deco looking bullets of silver. These cars are revered by the twisted and the shaman's rituals take place near the switching control panels. Once the power is turned on the Buzzing will instruct the shamans how to operate the cars and switches - the Twisted will begin travelling about the valley.
If the PCs are able to make use of the rails for themselves they will be able to travel about the valley at high speeds - unless they hit one of the few places where the rails have been covered or damaged.