Meaning of "as ... as any ... someone had ever done"
Your first interpretation is almost right. It means he'd never traversed stairs steeper than these. (It's odd, however, to speak of 'traversing' stairs.)
Meaning of "as ... as any ... someone had ever done"
Your first interpretation is almost right. It means he'd never traversed stairs steeper than these. (It's odd, however, to speak of 'traversing' stairs.)