A grueling physical workout intended to make you a better athlete. Usually done at home or the gym, and we call that place the "pain cave."
"If I want to get faster on the bike, I've gotta do my workout, so I am headed to the pain cave."
A situation that involves either performing tasks for or working with people you do not like.
Question: "How was work today?"
Answer: "It was a total pain cave..."
A mentally and/or physically debilitating condition worse than a hang over usually brought on by the consumption of copious amounts of alcohol combined with severe lack of sleep.
... oh my head... it's a day in the pain cave for me today, thanks to that goddamn moonshine!
Dark room or basement where you lure unsuspecting and intoxicated women.
Come into my pain cave so I can bludgeon you.