At this month's meeting of the Hollin Hills Orchid Society, we made terrariums!
There is a next of sphagmum moss, then from the bottom up, a layer of horticultural charcoal, perlite, peat moss, and some orchid bark. I've stuck a couple of dendrobium nobiles in along with a leaf from an African violet (those things can root from a leaf!), and some companion filler plants! I need to keep it out of direct sunlight so that I don't boil everything in the glass so it's sitting by one of the south facing windows but slightly away from the window.
It normally takes 2-3 months for terrariums to settle in so I will report back! As it's settling in, I'm going to keep some plastic wrap on top to really keep the humidity in. If this works out, it is very tempting to make another one (or two or five) with miniature orchids!