I found this $12 hand-blown Polish glass canister and thought it looked the part for a terrarium, so I put one together yesterday.
The base stratum is clays balls to absorb water and create a "groundwater" space on the bottom.
A screen over the clay balls keeps out the soil, which is a tropical mix mostly made out of coconut husk.
The three plants are a maiden hair fern, some sort of small groundcover vine with tiny leaves, and a carnivorous pitcher plant. We shall see what lives.