bottomless ravine; abyss
Literary expression for an extremely deep, seemingly bottomless valley.
He felt despair as if falling into a bottomless abyss.
深淵 is a more common word for 'abyss', while 万尋の谷 is a classical, metaphorical expression.
Standard kanji spelling.
Variant using 仞 (a unit of depth).
From 万 (ten thousand) + 尋 (a unit of depth, about 1.8 meters) + 谷 (valley), literally 'valley of ten thousand fathoms'.