Retrogaming is going into your attic (or basement) digging out that old trashed
Atari 2600 or
NES, hooking it up to your
TV, plugging in a cart, and being utterly disappointed.
Since you probably have some old console sitting in your abode (or can find a decent emulator) it's a pretty cheap hobby. On eBay, however, bring a fat checkbook.
Popular retrogaming systems:
Atari 2600
Colecovision Commodore 64
NES Intellivision