Sra. Cole no orfanato deixou escapar que havia uma caverna do mar perto de onde os órfãos foram levados em férias de verãoL:
‘But I’m jiggered if I know how he got up there to do it. All I know is he and Billy had argued the day before. And then –’ Mrs Cole took another swig of gin, slopping a little over her chin this time, ‘on the summer outing – we take them out, you know, once a year, to the countryside or to the seaside – well, Amy Benson and Dennis Bishop were never quite right afterwards, and all we ever got out of them was that they’d gone into a cave with Tom Riddle. He swore they’d just gone exploring, but something happened in there, I’m sure of it. And, well, there have been a lot of things, funny things ...’
She looked at Dumbledore again, and though her cheeks were flushed, her gaze was steady.
Half-Blood Prince - page 251 - Bloomsbury - chapter thirteen, The Secret Riddle
Dumbledore passou boa parte do Príncipe Mestiço saindo e procurando por Horcruxes. Sabendo que Tom Riddle havia usado uma caverna do mar para aterrorizar seus companheiros órfãos, deu-lhe uma pista para, pelo menos, começar a procurar por cavernas marítimas apropriadas. E finalmente ele encontrou o caminho certo:
‘Lumos,’ said Dumbledore, as he reached the boulder closest to the cliff face. A thousand flecks of golden light sparkled upon the dark surface of the water a few feet below where he crouched; the black wall of rock beside him was illuminated too.
‘You see?’ said Dumbledore quietly, holding his wand a little higher.
Harry saw a fissure in the cliff into which dark water was swirling.
Half-Blood Prince - page 520 - Bloomsbury - chapter twenty-six, The Cave
É quando Dumbledore e Harry encontram a caverna do mar. Dumbledore também sente que a caverna tem uma magia conhecida e determina que Tom Riddle já esteve lá.
‘How did you know that was there?’ Harry asked in astonishment.
‘Magic always leaves traces,’ said Dumbledore, as the boat hit the bank with a gentle bump, ‘sometimes very distinctive traces. I taught Tom Riddle. I know his style.’
Half-Blood Prince - page 527 - Bloomsbury - chapter twenty-six, The Cave