Pandora's box

These 2 are OK:

It is like opening Pandora's box.
It is like opening a Pandora's box.

The one with "the" would be all right in certain very specific contexts, for example:

I was searching around in an attic and came across an old trunk of my grandfather's. It was securely locked and I with great difficulty opened it. No wonder it was locked. Inside I found documents that showed he came into this country illegally, that he was imprisoned in his native land, and that he h

No, that won`t work, Summit. 'Pandora's' remains a possessive there, which cannot co-exist with 'the' determiner. 'It was like opening Pandora's box / a Pandora's box.

There's no problem grammatically with using "the" with a possessive, as in "I opened the captain's trunk." The "the" in the example is okay because it is "the" trunk, which is like "the" box.

My mistake: it is the proper noun that cannot take the article. You cannot say (X) 'I opened the Captain Queeg's trunk.'

Thanks Mister Micawber, but can you please explain how "opening a Pandora's box " is correct?

We can and do use the indefinite article when referring to an item that resembles the original item:

I carved an Eiffel Tower out of ice at the Ice Festival.
He is a real Don Juan with the ladies.
Everyone has an Achilles' heel.
You're just a Scrooge!

Oh, OK.
Thank you!

I'd like to look back at Anon (Summit's) earlier post presenting a use with 'the', because it finally dawned on me what he was getting at: I agree that under limited conditions 'the' is possible when speaker or listener already realizes the metaphor. I'd like to re-work Summit's example to make this clearer:

I was searching around in an attic and came across a mysterious old trunk of

Wow! Thanks, I'd have never thought of it