A large spool of finest spider silk, untouched by the ravages of time and the inferno that roared through these ruins. Clearly something special, likely meant by these ancient spider-farmers for sale or use in some wondrous creation.
The thread itself is nigh unbreakable, hard to cut, and a bit elastic (though not sticky… how would you unspool it?). I’m sure you could come up with all sorts of clever uses for it.
For a mere pittance (say, 500 coin, less your Charisma), you could commission a master artisan to weave it into a stylish, form-fitting garment (worn, 0 weight) that grants 2 Armor against attacks that cut or stab and ignores the piercing tag. Oh, and did I mention that it will never burn?
Worth every penny, I’d say.