Trophonius

Trophonius was a Greek hero worshipped at Lebadea in Boeotia, where his underground oracle was one of the most famous in Greece. According to legend he and his brother Agamedes built the temple of Apollo at Delphi. Those consulting him underwent purification rites before descending into a narrow chamber, from which they were said to emerge terrified; Pausanias, who consulted the oracle, left a detailed description.