That's where the screenshot key comes in handy
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What I like to do is walk around maps that I find inspiration from and screenshot areas that look good to me, along with screenshotting the lights, doors, floors, walls....all sorts of parts of the map to draw inspiration from whilst mapping.
On the topic...prop models can make decent levels look great. For example, trash models in a city street level can really add to the detail, while paper and pen/pencil models could add to an office level. Just don't go over the top with their implementation.