Coconut Cave Hideout These caves are made of Real Natural Coconut shells. These provide your pet a secure hiding place and relieve pressure. The shells can be used in wet or dry environment. These are great for skittish/shy animals. Also perfect for nocturnal pets. Ideal decoration for your tank, creating a natural environment making your pets comfortable. Diameter is about 4.5 inches. Opening varies from 1.5 inches to 2.5 inches. Note: Both inside and outside of these coconut shells have been cleaned. No chemicals added or used in cleaning process. Shined shells are done with mechanical polishing with wheels.