Table (King's Ransom)

You seek the grail of old,
but no longer is it a goblet of gold.
Among these nine will you find what you seek,
but be careful and don't peek!
A wrong choice will expel you,
so consider carefully each clue.

Three boxes contain only air,
beware of three boxes, for danger lurks there.
Two hold only rubbish but would fool you with disguise,
only one box holds your prize.

Clues will give the information you need,
rubbish always sits to the right of danger, pay heed.
There is nothing helpful in boxes great in height,
and boxes on either end will not end your plight.
A tall or small box will only bring you anger,
but a square box will not put you in danger.