Alternate port websites

I like to consider myself in tune with 'Underground' culture (although as I've aged I'm sure I've lost touch somewhat). I've always wondered if there was a whole hidden universe on the internet that wasn't being served on port 80. It seems like a fairly simple way to keep a website underground as most internet users probably aren't even aware that there's a port setting involved when they visit a website. Anyone out there know of any websites being served on a port other that 80/443?