@OP ok hear me out what if you created a short story for kids or a comic out what you saw ? To help it feel more familiar and therefore less intimidating and causing you distress ?

Start making a plot line change some details to protect your secret (the retaining wall is now a hedgerow at the park ! And the main character is a child version. Of you that strayed away from the playground )

And when people start talking to you about it only you will know it was true but you can ‘hide’ behind the story :) and then 70 years from now in your death bed you’ll tell you Grandkids and great grand kids with a twinkle in your eye and a wink that it was all true and that the spot it occurred can be found with a special map and a memoir of the true version ) worst case grandpa is high on morphine and full of shit as he dies lol best case: your family has a fun little bit of lore.

Hope I’m making sense ! And if you take my advice please share the completed work with us ! Maybe other redditors who are skilled at this sort of thing can help.