I have become terrarium obsessed. It started a few years ago, but I couldn't find a lot of info on them. Now there's terrarium sites and books and whatever everywhere...but most have bad info, so take what you read with a grain of salt. Once I got a handle on the how-to part, I've made some lovely grown up ones.
Naturally, the Peanut wanted to make one with me, so we did this one for her pig themed birthday party. We used a barn, barn animals and fence we gave out as the "goody bag" for one of her birthdays. I put some extra aquarium gravel we had laying around on the bottom. Sprinkled it with charcoal...easily found at Walmart or a pet store. Then I covered the potting soil with moss I found in the back yard.
The rocks, slate and all the plants were also found in our backyard. The big plant we had in the back right corner died...hence the reason it looks empty and brown. But since I grabbed moss surrounded by weeds, there are constantly new plants growing in there. At least once a week she's yelling out, "Mommy! Come look!" because something new sprouted.
Maybe it's not super fancy, but this one has certainly been the most fun!