There is a mirror that gradually lowers the temperature of whatever it reflects.  They thought it could be safely contained by simply locking it up in a dark room and forgetting about it.  The thing is, truly and completely blocking all light out of a space is far harder than one might expect.  A few stray photons inevitably leak in through; to say nothing of light outside the visible spectrum. It wasn’t much, but a century and a half left unattended was enough to eventually freeze a wall until it became brittle and collapsed.  

The collapsed wall set off a domino effect of objects and entities breaching containment.  By the time they sent me in with an inventory manifest that some paper pusher extracted from a deep archive to see what I could salvage from the situation, the antique building full of anomalous artifacts had been reduced to rubble.  The mirror somehow survived though. 

These days we’re more sophisticated about our containment procedures. Sure, we’re still ultimately locking the mirror in a dark room and forgetting about it, but now the walls are insulated with built-in heating elements, the mirror’s positioned on a constantly rotating dais so no one spot gets too much prolonged focus, and the whole chamber is lined with sensors monitored by a computer that will alert someone if temperatures ever get outside designated ranges. 

I like to check up on the mirror from time to time.  I’m the one who brought it in and I’ve always been prone to sentimentality.  And you have to admit, it is kind of cool.