I would imagine something similar to a regular playground but with adult sized equipment.
Near to where I live there's a park with light exercise stuff for old people, like pedals in front of benches or wheels to turn using a crank or handle.
An adult-size playground where everything's built for a larger person and all of the climbing toys that got removed sometime in the 80s-90s timeframe because of legal liability are back, too.
I'd pay good money, and sign whatever necessary, to get to relive the latter part of your third point. So many fun things got removed, not all of it for good reason....
I would hope that it would just be a playground just for adults. Don't know why people just lose their spark for playground shenanigans in age. I would love to climb and jump around again. But there isn't any place for that for adults.
I don't know if it's still there, but when I visited the town of Ayr in Scotland about 25-ish years ago, they had a playground very similar to that right off of the beach. Everything was large enough to accommodate adults, and I think it may have actually been castle themed. No ball pit though. They did have a thing like a tilted merry-go-round that was at waist height and had no handles. Not sure what it's called, but it was probably the funnest and most dangerous single piece of playground equipment I think I've ever come across. There were about a dozen of us traveling together, and I don't think a single one of us walked away from that thing without catching a boot to the face at least once.
It would depend on the context. If I saw it on PornHub, I'd assume something related to porn. If I saw it in a flyer from the local Parks & Rec department, I'd think it was a standard children's playground, but for adults.
So basically like Chuck E. Cheese or discovery zone from the 90s. Ball pits jungle gyms. Oooo or some American gladiator(especially the tennis ball guns) or ninja warrior type courses
A playground designed for a nursing home but actually good.
Maybe have a boxing station for bone health, a pool for low impact body movement and a kids playground in the corner to help keep the adults feeling safe and connected to their community by seeing the next generation running around laughing, screaming and having fun.
I think the Adult tag has been coopted to mean sex stuff. We did go do ziplines once, that was like a playground for grownups in a way, they don't use Adult in their marketing.