A strange patch of cement in the center of the basement that is actually the 12th dimensional flesh of some creature that cannot be fathomed. The space in the basement will pucker like a red infected zit blister and a small turd like excretion will appear. Foul in taste and smell but toxick in a way that produced visions of nearby universes and leaves a residual power, most commonly a sexual prowess that allows the worshipers to perform carnal activities until they can again glimpse these worlds.
This act of worship is not technically unspeakable...but no one really wants to talk about it...nor hear about it. The breath almost invariable smells like dog shit on your shoe for days...and comes and goes...so you can never be sure when you are going to smell.