If you have no other use then why not make a planter out of it, as far as drilling holes, cast iron is relatively soft and drills easily, a small electric drill will do the trick, drill the holes first then use a primer and a good Rust Oleum type of paint.
If you don't want to drill then realize that plants in containers with no drainage do sometime suffer from stagnation problems and root rot.
You can always use artificial flower/shrubs,leaves in it and keep it in a covered location so not to cause any damage, We have several large stoneware crock in our home which we use for various purposes, We have a tall butter churn crock that has artificial grasses and leaves in it and it looks very nice next to our inside stairwell, we use a large 6 gallon sanitary stoneware crock which I made a wooden lid for and we use it for dog food in our pantry, we have another large crock on our heart which holds fire starters,matches and kindling and my gloves for opening the lid on my wood stove, I also have one of those 3 leg bulge pots on the heart filled with fatwood strips.
Let your imagination run wild, an old cast iron scotch bowl or crock filled with fruit on the counter or table can make a lovely but useful container.
