Hardest trail ever ridden?
The uncompromising, take your life in your hands, come rain or shine, sheer mind killing crapness of it daily commute to work. Funnily enough, in contrast, the ride home is the easiest!!
I suppose when I think of “hard” in the context of riding I immediately equate hard with mentally draining/challenging, or difficult to maintain the motivation for, whereas any good or unknown trail might be physically demanding, physical pain is generally short-lived and easy to ignore, and as long as it doesn’t form part if the daily grind, all other riding is all good.