Actually, this one hasn't been forgotten at all. I was delighted to discover, when poking around the Internet, that lots of people remember it as fondly as I do. There's even a nice Wikipedia article with a complete plot summary that will save me the trouble of writing one. Briefly, you have ballooning, riches beyond your wildest dreams, a trip around the world in 40 days, and the biggest explosion in history. How can you resist?
The 21 Balloons was published in 1947 and won a Newbery award. I probably read it a year or two after that, and I was astounded and delighted, so much so that I read it several times over the years of my childhood. A few years ago, I bought a used copy and was astounded and delighted all over again. Maybe you will be, too, if you choose to read it.