Music visualisers are -- how can I put this -- quite '90s. But this one takes an MP3 and renders it into a fly-through of a constantly changing landscape. It's still quite '90s, but it's also weirdly, amazingly compelling.
Like some kind of flight sim that reacts to the pulse of your music, it's incredibly easy to sit and stare at it for tens of minutes on end. If you're wearing headphones in the office, people may well wonder what's happened to you. There are also two other visualisers; one looks like a volcano, the other some kind of weird '80s dream sequence. All are great fun.