Necklace of Skulls (Virtual Reality Adventure #4) by daelsepara

Learning of the disappearance of your twin brother in the trackless desert, you resolve to set out and discover his fate. Leaving the hub of your elaborate Mayan civilization far behind, your quest takes you to the lost jungle cities, across mountains and seas, and even to the baleful depths of the underworld. If you are luck enough to survive the treacherous desert journey, you must still confront the wizard called Necklace of Skulls in a deadly contest whose stakes are nothing less than your own soul.

This is an unofficial adaptation of the "Necklace of Skulls" Virtual Reality Adventure game book by Dave Morris. Adapted with permission from Dave Morris.