Secreted beneath the campus of Piula Methodist Theological College, Piula Cave Pool consists of two blue-green, fish-filled freshwater grottoes, only metres from the sea. The brave can swim between them via a creepy 3m underwater passage that's difficult to find in the darkness. The pools are concreted in so it’s not a completely au naturel experience but it is refreshing and the college grounds are beautiful.
From Apia, take the Falefa or Lalomanu bus (ST4).