I know this is a longshot...but someone out there must know this.
I grew up in American University Park in DC, right off Mass Ave by Chevy Chase, etc... I recall, and even have a photo somewhere, of a house, somewhere near my own home, that was built to resemble a mushroom, color and all. All I can remember is that it was near to Westmorland Circle, possible off River Road. Help!
My second memory needing jogging is the Castle House, somewhere around Rock Creek Park by Silver Spring. I know it was there, I remember driving up to it, then walking onto the property, and seeing the moat and all.