A closed glass terrarium is a miniature planet: the water inside never leaves, it only changes form. This 2D cross-section models that cycle directly — soil moisture evaporates faster when the light/heat slider drives up soil temperature, the plant transpires moisture from its roots through its leaves, and the rising vapor condenses into droplets on the glass walls the moment the interior air holds more water than the cooler glass surface can support. Droplets grow, slide down the glass, and return to the soil, closing the loop. Watch the humidity and temperature readouts settle toward equilibrium, and push the light slider to see the balance shift between fast evaporation and steady condensation.