Shape the modeling clay into a mountain. Flatten the top of the mountain. Place the mountain against one side of the box and slope the side facing into the box.
Line the bottom of the plant container with about 1 inch of small stones. Place a 1/2-inch layer of activated charcoal on top of the stones. Lay a thin layer of sphagnum moss over the charcoal to prevent the soil from falling down around the stones.
Place a 2- to 3-inch layer of potting soil on top of the sphagnum moss. Use a pencil or similar object to make depressions for the plants. Put the plants in the holes and gently pat the soil around the plant.
Position the plant container away from the mountain. If you are placing a turtle in the box, build land area using the sand. Slope the sand so the turtle can easily climb onto the land. Add decorations, if desired.
Add very warm water to the box to cover about one-fourth of the mountain. Poke about 10 holes in the bottom of the plastic cup of ice. Put it on top of the mountain.
Cover the box with plastic wrap and secure with a rubber band. Place the box in a sunny window, or turn on the lamp and aim the light down into the box.
Observe the water cycle box periodically throughout the first day. Record your observations. Continue to observe the box, once or twice a day, for a month or longer. If you included a turtle, feed it regularly and care for it according to instructions from the pet store. If you added snails, you can feed them leaves, plant bark, algae and limestone or chalk. Add water if the box dries out from opening it to feed the turtle or snails. Open the box a little if it is too wet.