A tunnel, a diary and a memory.....

[Tim]

No: HPFGUIDX 113883

> But I wasn't 
> going to waste those long years I'd spent searching for it. I decided 
> to /leave behind/ a diary, preserving my sixteen-year-old in its 
> pages so that one day, with luck, I would be able to lead another in 
> my footsteps and finish Salazar Slytherin's noble work."'
> 
> (COS "The Heir of Slytherin" p.230 UK edition) - my emphasis.

Tim now:

 Perhaps it was left behind in the same manner as the Maraders Map. Handed down from 
one student to another.