Possible Clues:

• Got about the decay of the sound of the whole of it
• Capri's is blue
• Had no choice with river entering cave
• A picturesque cave as in Lourdes (6)
• Capri has a famous one
• Cave's deterioration — got crumbling walls
• Cave reached round river
• In the rock the hole may go to and fro at last
• Must have resistance inside cave
• Cave reached crossing river