The author proposes creating an interactive scavenger hunt app using Nexmo's Voice and SMS APIs, Express, and Node.js. To start, users need to create a Vonage account, purchase a Nexmo phone number, and set up a Nexmo voice application. They then link their phone number to the application, generating QR codes that lead to a Glitch project. The app allows users to record clues, which are stored in an asset file on Glitch. When a user scans a clue with their smartphone, the app sends an SMS to the designated Nexmo number, and upon receiving the message, the phone makes a call to play the next clue's audio recording. The game continues until all clues have been found, providing a fun and engaging way for users to explore their city or neighborhood.