That must be
Reasoning:
Sunken land evoking galleon (8)
meander
twisted course: def., and then "me" + "under". The geology of underworld rivers isn't known to me.
I went for "meander" first (trying to avoid getting lost on the Onion Sea), sought to explain "Bacchus" via "renamed", but the clue would not fit this, and I went on a wild search for other solutions. Maybe "twisted" alone is the definition, and "course for Bacchus" means "wine", and "below" means "sub-" -- now make something of it; maybe "twisted course" means "source"; maybe "Acheron" must be built after all. Then I realized the homophones -- and that "Bacchus", in a double role, might encourage drunken reasoning. (It's almost an anagram of "maenad", too; if only.)
I went for "meander" first (trying to avoid getting lost on the Onion Sea), sought to explain "Bacchus" via "renamed", but the clue would not fit this, and I went on a wild search for other solutions. Maybe "twisted" alone is the definition, and "course for Bacchus" means "wine", and "below" means "sub-" -- now make something of it; maybe "twisted course" means "source"; maybe "Acheron" must be built after all. Then I realized the homophones -- and that "Bacchus", in a double role, might encourage drunken reasoning. (It's almost an anagram of "maenad", too; if only.)
Sunken land evoking galleon (8)