400 metres to the bottom, 深达400多米

2. an inner world where only the most adventurous dare to go.
   一个只有最勇敢者 才敢涉足的地底世界
3. Beneath our feet are countless miles of cave shafts and passages.
   我们脚下有着绵延不绝的洞窟和隧道
4. The Cave of Swallows in Mexico,
   墨西哥境内的燕子洞
5. 400 metres to the bottom,
   深达400多米
6. deep enough to engulf the Empire State Building.
   足以吞没整座帝国大厦
7. This is the biggest cave shaft in the world.
   这是世界上最大的深洞
8. Yet these depths were first explored only two years before man landed on the moon.
   然而人类直到登月前两年 才第一次进入这个深渊

来自《行星地球 第一季 第四集 Planet Earth S01E04 洞穴》第 5 行