Silly Saturday: Weird Plant in the Garden!

I spent most of the lovely sunny afternoon clearing a corner of our garden which hasn't been touched for some years and was very overgrown. During this I came across this weird plant almost completely buried in the soil - I'm feeling rather silly as I've no idea what it is. In fact it looks rather silly itself!

It seems to have a large round tuber about 10-15 cm in diameter and about 5-6 cm thick. At first we thought it was a stone with some roots and stalks stuck to it, but I cut in half with the spade as you can see; it was firm but easy to cut, with very white, slightly damp flesh inside. The roots look quite normal but some of the stalks are tightly curled into spirals and there are some some little fruit-like reddish spheres on soem fo the stalks about 1cm or less in diameter. I've made a triptych of 3 views of it lying on our rusty old garden roller - on the middle one I've turned the right-side half upside down.

Does anyone know what it is? If everyone says, "Of course it's a xxxxx" then I'll feel very silly indeed. I reckon it definitely fits admirer's fun Silly Saturday challenge anyway.