If you have an exotic cat rescue facility nearby, they sometimes put bowling balls in with the tigers and lions. It's one of the few toys they can't easily destroy.
Maybe there are more of them in Central Texas, when this area is not reminding me of the south of France; it often reminds me of Africa. Anyway, I do know of a few around here. There also is/was one in my backyard. The enclosure is still there, just been blessedly empty for years now. It's quite sturdy, heavy gauge chain link, chain link "roof", and just over 700 square feet. There is a separate lockout cage with a guillotine door. It includes a cairn (you could look it up) and a huge timber about 6' off the ground that the cats enjoyed resting on. It also gave them a good place to watch for prey. The goats quit coming around.
I think now it would be a great place for a garden, the deer would not be able to nibble in there.
Getting back on topic, I don't think I ever put a bowling ball in there. I gave the cats coconuts to bounce around, and on special occasions a pinata, they loved to tear those up.
A cairn is a typical word from Lord of the Rings....
There are several big cat rescue places in the Sacramento CA area.
Too many people are so clueless that they go out and buy on the black market cute little Tiger cubs or Lion cubs as pets. Then in a year or so these people are astonished to find out that "kitty" weighs 300 pounds and is killing the neighbors. These poor cats end up in big cat rescue places.
Fluffy Pumpkin is a handful at times weighing 20 pounds. I can only imagine what a big cat would be like.
Another continual problem is people who decide they have some special rapport with the critters, and they go in the cage. These fools often die, and I'm quite sure it's not peaceful.
Jay, I know what hikers (quite correctly) call a "cairn"....a stack of fist sized rocks usually. What I built was more "ancient monument" style; 3 boulders with a huge flat slab of rock on top. It was done the old fashioned way, with a forklift.
Tell your sister it's the sort of thing that sometimes protected burial sites.