Lisa Gilbert grew up building forts in her backyard with neighborhood kids. Now that she’s co-coordinator of AMC’s A Mountain Classroom, her backyard is a national forest and the children she’s building with arrive by car or bus. As she leads programs out of the Highland Center and Cardigan Lodge, she’s infusing fort-building with environmental purpose, teaching children about habitats and ecosystems and about how to “leave no trace” when they head back home.

“It’s a good way to get them to explore,” she says. “They love looking for materials, and thinking about how nests, dens, burrows, and other homes are built.”

Here are her suggestions for constructing a nature-friendly fort.

1. Location, Location, Location. When out in the woods, pick a spot that is not visible from the trail so you don’t affect other hikers’ views. Find an area with packed dirt so you have less effect on wildflowers and other plants. And stay 200 feet away from water (Gilbert recommends “80 adult steps or 100 kids’ steps” as an easy way to measure this). Also, try to avoid blocking animal nests or burrows, so that parent animals aren’t kept from their young. To make sure a site is good, “We have kids get down on the ground, look up in the trees, look all around,” Gilbert says. 
2. A Strong Foundation. Within your general area, find a spot that will be good for building. “I like to look for a big boulder or a fallen log you can lean it all on, in a lean-to way,” Gilbert says. “That’s easier than freestanding.” 
3. Dead and Down. Tell children to collect only natural objects that are already “dead and down” on the ground—no pulling bark off trees or picking flowers. Set a boundary for the area in which kids can gather their material. If you intend to ask them to put things back in the same spots later, get them thinking now about where they found that big stick. Also ask children to look in different directions, so they spread out and don’t beat a trail into the earth. 
4. Build and Decorate. Once the children have created a basic lean-to with fallen branches leaning on a rock or tree, encourage them to find beautiful decorations for the entryway: special leaves, rocks with glittering mica, or sticks with patterns left by bark beetles, for example. 
5. Move-In Time. Let the kids try out their creation and talk about how different it is from the habitats they usually live in. For a group of eight kids, Gilbert says you need a “long, skinny fort”: “They crawl in and sit with their knees to their chins to see if they all can fit.” 
6. Leave No Trace. Once you’re done playing, involve the children in dismantling their own fort. Sometimes this can be after a few days, sometimes after a few hours. It’s important to explain that all the materials are part of the habitat for the area’s wildlife—that “salamanders are literally living under those sticks,” as Gilbert says—so leaving the area disturbed may affect them. Once the main materials are scattered, kids should “fluff the duff”—gently scatter and fluff up the pine needles and leaves that have been flattened by human feet. “That can be a game in itself—trying to make it so no one knows you were there.” 

Gilbert’s tips reflect her own experience in the mountains, but she emphasizes that “this is something you can do anywhere.” When she built forts as a kid, she sometimes used an old piece of plywood or a plastic chair, or a tarp for a wall. Families might also add large cardboard boxes to a structure. “You can fit it to whatever you have,” she says. “If you aren’t in a big forest, it’s going to be hard to find enough dead and down materials.”