Vile Lair & Mehrune's Razor

I recently bought the Nights of the Nine add on disc which included a bunch of minor mods (Orrery, Thieves Den, Horse Armor, etc). New to me was the Vile Lair. Since I've already completed the main quest, been a vampire/been cured, etc. I was confused as to what Vile Lair is supposed to be? Is is a Dark Brotherhood lair or a Vampire Lair? Maybe a bit of both? What is the Ichor of Sithis for? The other special ingredient that you find appears to be an alternate cure for vampirism. Is this correct? What are you supposed to do with this place? I guess if you are playing a vampire its a safe haven and a place to rest and suck on "human cattle" blood. The book found there appears to indicate that Sithis is unhappy with you (because of vampirism?) and that you should take some sort of action. Appreciate any info as it will be a long time before I replay this marathon game.

Also in Mehrunes Razor you find some weird ingredients - Chokeberries and Beating Heart in particular. Tried taking them but the effects were not desireable. I think the Beating Heart just turns you into a vampire, but I'm not sure. The Chokeberries just seem to give you a disease with some nasty side affects. Anything else to do with these things other than avoid using them?