MapGuess normally works with no setup. If you're seeing this, the site's free monthly Street View quota is probably used up (or Google Maps couldn't load).
You can still play: try Demo Mode below, or bring your own Google Maps API key — create one in Google Cloud Console → Credentials, enable Maps JavaScript API + Geocoding API, and restrict it to this site.
Your key stays in your browser (localStorage). Demo mode uses a mock panorama so you can test the UI without Maps.