You might have looked at ballards* and thought There's no point trying to balance things on top of something so round. But on my morning walk, I saw that someone had precariously balanced a stack of those rolly-spooly-seat thingies† atop a ballard, taking advantage of the seat's concavity.
*Ball-shaped bollards
†Do those seats have a name? I thought they might be called "rolling chairs" to contrast with "rocking chairs" but apparently a rolling chair is something else entirely. [Updated to add:: Apparently they are "spun chairs"]
