Senza no Iwaya千座の岩屋The place where the AR annotation was kept displayed for 3 hours on 3 consecutive days to trigger the 'Kimishima Report No.3' flag. Reportedly, the tide does not stay out for 3 hours unless it is a spring tide. Since you cannot (or can hardly) enter the cave when the tide is not low, plan your visit around low tide times.
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