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cave; tunnel
tunnel tomb (Kofun period)
山腹に横穴が幾つも掘られていた。
Several horizontal caves had been dug into the mountainside.
古代の横穴式住居が発掘された。
An ancient cave-style dwelling was excavated.
子どもたちは横穴を探検して遊んだ。
The children played by exploring the cave.