OK, this one may seem kind of boring, but it doesn't have to be. Plenty of guys have offices in their homes -- you might not think of it as a man cave, but isn't that exactly what it is? It might not involve a TV or a bar, but anyplace you go to be alone can technically be defined as a man cave. And there's no reason that a home office has to be a dull, sterile place. A TV may not be appropriate if you actually have to work there, but invest in a comfy leather chair, install relaxing lighting and surround yourself with memorabilia. Make it a room you like to visit instead of somewhere you have to go.
Must-have: This might be the only kind of man cave that features actual books.