Isn't it incredible how the word "spell" encompasses so much?
1) to make a word letter-by-letter... as in, to spell a word... spelling bee and all that...
2) a series of words that has magical powers- a spell; and
3) a state of enchantment, under a spell.
With all of that in mind, Oliver turned the word "spellwork" into its plural, Spellworks, in the tradition of "ironworks" where the singular is the same word as the plural, and the name of the place is the same word as what happens there.
Spellworks is a hub of magical practice that poetry can be, letter by letter.