To the reader? The world of your book is a black box. Devoid of all sensation—no sights, sounds, tastes, smells, or aural pleasantries beyond dialogue. It is up to you and your prowess of description to fill that world out—to let the reader experience it as you would have it experienced. Such power! Such responsibility.
If you do it right, you can grant readers the ultimate experience: the immersive feeling of actually being in another world. And trust me when I say readers will re-read the same book over and over again just to get that sensation, if you get it right. If you get it wrong, readers will at best set your book down and never pick it up again—and at worst, laugh in all the wrong places. No pressure, eh?
So—what goes into writing evocative descriptions? Strangely enough, it’s not just adjectives. It’s also character reactions, dead-on comparisons, and a sensory smorgasbord. (Not to mention point of view, pacing, structure, narrative distance, and the sounds of words, as those are addressed in entirely different articles.) And luckily, these things are pretty easy to put into practice, once you know what you’re looking for.
Show Don’t Tell
I know, I know! This is the oldest advice in the book. So old, it’s kind of cliché itself. But here’s the thing: it’s largely true (with notable exceptions, of course), and nowhere is it truer than in writing description. Writers often feel a powerful urge to make the reader feel exactly what they want them to feel—to make them experience the world exactly as they mean it to be experienced. And in doing so, new writers often make the mistake of telling us how to feel about everything that is being described—using authorially judgmental words—and symbolic words--instead of sensory, descriptive words.
For example: “The evil trees were scary and dumb looking.”