Lay the box down so the two ends are open. Thread yarn through one drinking straw and then through the nail hole and knot to secure it. Hang numerous straws, at various levels, in one area of the cave. Allow enough room for the students to wriggle around without touching them. Make the stalagmites by taping large plastic cups together end to end, or mouth to mouth.
Stalagmites can be one to three cups high.
Mark a trail with the stalagmites leading to one open end of the box, through it, and out the other end to represent an area of the cave where the explorer can stand upright. The cavers will need to crawl in the area represented by the box. Instruct the students that they are to be cavers exploring a little known cave. It is their responsibility to not damage any speoleothems. Briefly talk about stalactites and stalagmites, to familiarize the students with the terms.