Sue Opp Dept. One our non-majors biology class has been using is pretty successful. It is a very open lab. I was able to make them using baking dishes and microscope slides and silicone glue. Food, chemicals, ice, and or light, are put in the ends of the chambers.
Students then design their own experiment to determine what things planaria like and dislike.
Depending on the level of students you may need to discuss hypothesis testing, the need for controls, repetition, how many organisms are needed, writing methods than can be repeated, etc. We do the minimal amount of explaining so that students can trip through it.