In this activity, learners turn empty 2-liter bottles into a see-through compost container. Through the sides of the bottle, learners make weekly observations of decomposition over the course of several months. They can explore how moisture, air, temperature and light affect the process, vary the design of their bottle, and build more than one column to allow for different decomposing materials to be compared. The activity comes from a printed book that is also available in Spanish, though the Spanish versions are not available online.