I like seeing photos of people's handiwork in the Aussie mancaves Facebook page. Here's a good one I saw recently of an old shed turned into a backyard pub.
Here's my dream man cave - this guy in the states set up his own retro video game arcade in a barn. It has over 50 machines.
Edit: Looks like Gizmodo has killed the link to the story. All I could find was the opening preamble...
Peter Hirschberg has just finished his stunning retro-gaming heaven, a Valhalla for the best arcade video games ever. His Luna City Arcade has 57 fully-restored arcade classics, which span from Asteroids to Zaxxon, plus a whole load of pinballs. Amazingly enough, he does all this on his own dime, for the love of it. This personal museum is open now to the public by invitation only, and the best thing: entrance and quarters are completely free for his guests.
I've heard that @NickM has a shared inner-city workshop. Care to share some photos that might inspire other members of the community, Nick?
He has pinballs too @Jackson.
Here's a couple more pix. A Flash Gordon pinball would be pretty rad.
There was an awesome bar and carport conversion at this house in Heidleberg Heights, but I think the realestate agent thought it was tacky and didn't include it on the images, you can just see it poking out of one of the images: