A question
How did they build a tunnel under the sea?
A calm, true answer. Then, if the wondering keeps going, the whole episode.
The short answer
They never dug down through the water. They started on land on both sides and bored sideways through a layer of soft chalk beneath the seafloor, which water does not easily pass through.
Two teams dug toward each other for years, one from England and one from France. When they met in the middle they were off by only centimetres. Trains now cross underneath the sea in about half an hour.
Go deeper tonight
The Chunnel: A Train Ride Beneath the Sea
The full episode, in one calm voice, with nothing that startles.
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Sleep timer
Read the guide for this one in the morning.
This connects to
One idea turns up in many different nights. Follow one and the library starts to join up.