a narrow sanctified cavern and grotto that may be entered with difficulty
やっと潜りこめるほどの洞穴や石室 - EDR日英対訳辞書
The swimming pool must've turned into the blue grotto of capri. 水泳場はおそらくカプリ島の青の洞窟に違いない - 映画・海外ドラマ英語字幕翻訳辞書
The swimming pool has to be the blue grotto on capri. 水泳場はおそらくカプリ島の青の洞窟に違いない - 映画・海外ドラマ英語字幕翻訳辞書
The paragraph on the Uka area of Izumo district in the "Izumo no Kuni Fudoki" (Regional Gazeteer of Izumo) records that there was a cave called Yomi no Saka (Yomi Slope) and/or Yomi no Ana (Yomi Cave); the entry reads as follows: "People cannot reach it, and do not know (its) true depth; and all those who reach this underground grotto in their dreams die without fail."
『出雲国風土記』出雲郡条の宇賀郷の項には黄泉の坂・黄泉の穴と呼ばれる洞窟の記載があり、「人不得不知深浅也夢至此磯窟之辺者必死」と記載されている。 - Wikipedia日英京都関連文書対訳コーパス