The setting here is a kind of fantastical imaginary landscape. It's a pretty spectacular one, populated by magnificent ships sailing away to far-off lands and knights trotting around on prancing horses. However, this poem doesn't actually represent a place, imaginary or no. Instead, it asks us to imagine imagination itself (whoa). That sounds totally confusing and way far out there, but think about it for a minute. The central metaphor of this poem asks us to compare reading a book to traveling to far-away places. The travel that goes on here is imaginary, and the speaker is asking us to summon up the idea of travel in our minds, not a specific voyage.