Meditating. You can kill hours and hours and it can vastly improve mental health, if you know how to, lol. :)
I've been attempting to meditate for months, I can't get past 3 minutes. Maybe I do it improper or something
Basically, the hardest part is to not get distracted, not even for a split second, lol. :) I've been trying for the past 8 years. The longest I can go without getting distracted is only 9 minutes, lol. :)
Distractions aren't much of a problem for me, but my mind wanders too much.