How to convert hard plastic kiddie pool into keyhole garden?

I 'inherited' a hard plastic kiddie pool from a neighbor and want to make a keyhole garden with it. It's the kind of pool with a built-up seat and step, rather than being just a round pool. I want to cut out that built up area plus a little more to have a path to the center of the pool. Oops, my only saw is the small gardening kind so I'll have to borrow one. Only, duh, I don't know what I need to do the job. Any ideas? Thanks, Annie

PS Please be descriptive. The only thing I know about saws is they have teeth. I guess whatever I borrow better have an operator to go with it.

Butterfly and Helln, I hope you read this. See where our discussion of lasagna gardening has led? Right now this pool is filled with all that sod I dug out for my veggie beds. I'm thinking that sod, laid grass side down, will make a really good first layer.
Can you tell it's been too rainy today to actually do anything so my mind has been spinning with ideas?