No worries. I've just discovered your response in my inbox (I've been having a bit of a year), which prompted me to go a wandering on the internet.

On Goodreads, I tried looking at at couple of similar books, and seeing what lists they were on. I found https://www.goodreads.com/list/show/79980.Armchair_Treasure_Hunts_, although I don't think that quite matches what you are after, and https://www.goodreads.com/list/show/133840.Best_Activity_Books, but didn't see anything there either.

The really frustrating thing is that there are aspects of this that sound really familiar, but I can't place it in time to work out when/where I would have read it.