There's that smell again...

As a bachelor in a semi-derelict flat, I'm used to the idea that my pad might whiff a bit.  It's a guy thing.  And a damp thing, a bike thing, and a surf thing.  But just lately, the smell has become a Smell, and last night it actually stopped me getting to sleep.  The reek was emanating from below my bed.  What ghastliness was down there?  I was worried the damp might be rotting my tatami, or that the sewer pipe from the bathroom had cracked.

( But it was more gruesome than that... )