Possible Clues:

• Underground column’s wasted time at POW camp
• Tiny POW? May be observed in a cave
• It's rising little by little, from POW camp might you say?
• One growing up in a cave
• Effect of dripping in prison on small child
• A mound of calcium carbonate - prison has me eating it
• In POW camp notes something on floor of underground passage
• Column made by dripping water
• Cylinder of calcium carbonate growing upward in a cave
• Upward-rising cave deposit