Underground riddle

From London Bridge to Green Park, and then Tottenham Court Road to Oval, I puzzled over Gerard Benson’s poem, Riddle.

The best answer I could come up with was The Word of God – resting amongst leaves – though it falters on the lines about entering a dark tunnel and being bathed in acid.

Internet searching reveals a better solution (stop reading, if you don’t want to know): the Apple of Eden.