Return to Atlantis is book 18 of the Choose Your Own Adventure series. It was written by R.A. Montgomery.
Three years ago, you led a deep sea expedition in search of the Lost City of Atlantis. You found it, but there's one problem: back above ground, no one really believed you. When your good friend Horton James III shows up at your office with funding and equipment, you jump at the chance to return to Atlantis. And this time, you are determined to bring back proof. There will be just one tiny problem. Getting proof of Atlantis may cost your life.