221 feet is the greatest depth..... below are some figures to give you an idea of what depths (literally) they had to go to:
Maximum depth below mean sea level Northern Line, just south of Waterloo...
Although a few parts of the network involved tunnels or underground hiding places, most of the "underground railroad" consisted of houses and farms of anti-slavery Southerners. They used these...
The term "underground" in underground railroad means secret. It also was not a road. It was more like a trail. So I guess if you were to say it literally, you would say "secret trail."
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