I don't know about Satanic cults in the area, however, Seattle is home to two of the largest BDSM/fetish/swinger groups in the entire country.
Psychology Today had an article about it last year. One group is named Center for Sex Positive Culture (CSPC), nicknamed the Wet Spot. It grew out of an underground coffee house. The last I heard, it had more than 10,000 members. A famous alum was Gary Ridgeway, the Green River Killer. The other is named New Horizons. The latter is located in a mansion in Lynnwood, just north of MLT. There isn't a lot of overlap between the two groups--in fact, there's a rivalry--so this means there are a lot of people into "the scene" in Puget Sound. There's also a kinky semi-rural resort near Redmond called The Longhouse, and it's no longer a secret that the "family nudist communities" have a BDSM element.
This next part is disturbing, especially for Stryker, and links shouldn't be read at work. Last year, the Seattle Erotic Art Festival, which is closely associated with CSPC, had a photography exhibition on "dark fetishes," which include "mummification," "water play" and "breath play." These can involve putting bags over people's heads,
submerging people underwater and/or leaving them restrained and alone in parks or rural areas for extended periods. For example, check out the interests in this
dark fetishist's profile. (Looks like he's on the Seattle waterfront.) Supposedly all of this is done "by consent," but there's also been some chatter in BDSM circles that not all sadists are bothering to
get proper consent. As an acquaintance who's into that scene wryly told me, "Consent is more of an ideal than a reality."