Clam shells. One day I'll have a big old daddy clam shell and I'll settle it into the dirt in the garden and fill it with water for the dog. Large ones are difficult to find and mega expensive as the clams are now protected in the wild and anything you'll come across is vintage or copies made of resin. In the meantime just a few baby shells. Biggest is 40cm. Bought these over the years at thrift stores for a few dollars. Maybe I'll stalk the neighbourhood looking for large shells hidden here and there in the gardens of the old houses.
P.S. Looks like I have a thing for large scallop shells as well :)