no one mentioned Berserk yet ? its one of the most epic adventure/fantasy manga and definitely not kiddy stuff
also vinland saga, lots of killing n blood and question about war n life
wolf guy - ookami no monshou, if you want something tragic (and dont confuse it other wolf guy titles manga)
what do you prefer more? action/battle oriented manga, mystery/suspense story, more pyshological stuff ? they usually have mix of those but some lean more toward one or the other.
some more title ive enjoyed : ajin, akame ga kill, ouroboros, claymore, jisatsutou. bakurano, promised neverland, fire punch
i used to read on mangafox but now i use either mangadex or mangarock
also some tip if you want a more adult type manga try to avoid typical shonen manga with stuff about friendship or such like fairy tail, naruto, etc
and beware of titles like berserk, hunter x hunter or d gray man, this trio is infamous for getting on prolonged hiatus.