Every now and then after a big rain these crop up in my basement. No obvious cracks or anything where they pop out of the unfinished concrete floor. I try to dispose of them without too much opportunity to shake of spores, and then douse the floor with bleach, but I also admire their ability to grow with no apparent nutrients.
When life gives you mushroom, make a mushroom farm !
I was watching all the cool things ecovative is making from mycelium and I admit I’m rather tempted. I have plenty of sawdust I could feed them.