Not sure if I have a definitive "happiest", but I know one of the happiest memories I have is pretty old.
When I was still a kid, during the brief time before I moved in which I had more than a single friend, my third friend and I were at a playground just hanging out. She lived in the middle of bumfuck nowhere in a small community with nothing more than 50 other (big) houses within a 20 mile radius of her house, so this playground was a bit of an anomaly.
Nevertheless, our parents felt safe enough to take us there, so we just played together for a while.
Then, when we were both getting a bit tired of chatting on the swings, my friend suggested we go take a walk in the woods.
The woods were, like, right there, mind. We weren't running away or anything.
I said "sure" because I was seriously up for anything other than swings, and so we went.
At first it was pretty sparse- the trees were a bit thin, there wasn't much to the place aside from some trash and broken twigs, but the further in we went the cooler things got. We saw this overgrown run-down carriage from god knows how long ago (at least a century? Or maybe there was some historical reenactment or something there lol), lots of different types of plants, even some weird-lookin' squirrels
but eventually it kind of just
stopped
the forest opened up into this huge plain with tall grass that went up to my chest
the place was big enough to induce a sense of scale but not small enough to feel claustrophobic- I could see the end of the plain something like half a mile away but only barely over the grass
the sky here was sunny and clear instead of grey and foggy like it'd been- felt like another world, almost. We must've gone super far out lol
All we could hear was the rustling of this (very) tall grass. No wildlife, no people. Most of what we could see consisted of the grass, the trees surrounding the clearing, and a big-ass rock in the middle of everything (seriously like 9 feet tall or something. Looked super tiny in comparison to the trees, though.)
I think it kind of unsettled my friend because she didn't stay long and we barely stuck around for more than a few minutes before she started towards whence we came. Which is fair enough, but I was busy having my breath taken away so I stayed as long as I could (not very long)
It was the first time I felt like i'd "discovered" something, even though I knew someone had been there before
the first time I'd kind of been alone (at least in terms of being separate from my family), someplace completely new to me and divorced from human civilization
It sort of hit me like a truck, and I wish that my friend hadn't dragged me out of the place so quickly lol
She was older than me and I wasn't listening to her, so I guess she felt like she had to take responsibility and get me out before I decided to live there or something
Anyways, yeah
After that we just went back through the forest, returned to the playground, got our ears chewed out for being gone so long, then parted ways
A lot of my other "happiest memories" are similar, now that I think of it
just me and something I personally value alone in some bumfuck nowhere creek or ravine or tree
either right next to a highway or far enough from normal people that I nearly got a missing persons report
maybe I should just go live in the woods when i can afford it lol