I recently got into fooling around on mg_ servers, which are basically servers whose maps are "mg"s, mini games. These minigames range around actual parkour, to deathrun, bunnyhopping maps, obstacle courses, etc.
Of course, I'd love to be able to play these maps by myself, but it doesn't seem like I can actually start a custom server with a custom map; it seems I'm restricted to Valve's official maps.
How do I play on a custom map? I'd like it so I can play offline if I need to, or online.