Terrariums are a fun outdoors project. Join me as I show you how to build a closed native terrarium in a sealed jar using moss, plants, hardscape, and insects found around the countryside, in parks or gardens. A terrariums is an enclosed ecosystem that can be self-sustaining, meaning you can have a slice of the natural world on your windowsill. They are great for relaxation, giving you a little chunk of nature to create and enjoy.