Topics are available everywhere. Any experience, place, emotion, or person is a potential topic for a descriptive essay. The descriptive essay is a way to transform the writer's personal perceptions into more universal communication; it is a way to broaden human experience to include the personal experiences or observations of someone in another walk of life than the reader.
The descriptive essay can illuminate an experience that you have undergone, for the benefit of someone else. For example, say you have suffered the loss of a brother or a parent to illness. Your ability to describe that experience, all of it, can offer hope to someone else in a similar situation, or help readers develop compassion for the suffering of others. When you write this essay, describe what you felt when the diagnosis was delivered, for example, and the process of illness and your response to it. Describe what you went through in the grieving process. Choose details from the process that crystallize the experience, rather than simply recount the events in order. You might focus in on a particular detail, anything that might reflect the whole experience. The smells in the sickroom, a particular trip to the hospital, even a seemingly unconnected observation, anything can provide material for the descriptive essay. Try to weave these details into a coherent picture.
Perhaps you want to write a descriptive essay about some quality you admire in another person, or that you want to cultivate in yourself. Perhaps your uncle or grandfather was an uncommonly honest man, the kind you'd like to be yourself or see more of in the population in general. You can describe events that illustrate this quality, or you could describe the ramrod straight posture that defined his trustworthiness. One event in his life can produce singular details that you will uncover as you research your topic. When you describe a praiseworthy personality, you illuminate and expand the influence of that person's goodness. Your praise for this person's special qualities can inspire your readers to reach for more in their own lives.
The events of daily life may seem to be mundane, but sometimes the small things of life can reveal the more profound processes beneath. In describing an event, say a first day at college, a writer will often uncover small, telling details that point to a larger truth. The weather that day, the worn steps leading to the illustrious lecture hall, your feelings of pride and confidence (or lack of them) all can tell a story that a reader will find enjoyable and instructive. Your ability to touch a chord of feeling in a reader depends on your ability to evoke and build on original observations in the moment. A writer can bring a reader into an event and make them a part of it, as if they had been there when it happened. In this way, the experience of one is added to the experience of many.
Choosing a topic for a descriptive essay is not as daunting as beginning writers may believe, since the essay's point may not be clear at first; simply choose any appealing thing, place, person, event, or activity, and begin to write. You may not know where your topic is leading, but as you write, the magic of the mind will begin to furnish ideas, details, and feelings; the result may surprise and delight you.