Pretty much all locations need something to stand on. We are accustomed to these being wood, worked stone, or the like. However, many adventuring locations take place in areas without the ability or need to have a medieval manufactured floor. For your caves, ruins, or even frontier homes and other buildings, there is the Packed Earth Map Set. Also useful as the muddy outskirts of a swamp or a clearing in a forested area. Great for standing, exploring, and potentially even digging in, but we wouldn't eat off it.
An alternative meaning to the phrase "Dirty Fighting", packed earth is a great backdrop for all your earthen needs, from underground caverns to vast forests and a whole lot more.