Greenwich Foot Tunnel

The tunnel created by Alexander Binnie in 1902 to cross the Thames river to Millwall in the north between Greenwich on the south coast. The tunnel has replaced an expensive and sometimes unreliable service that allows workers living south of the Thames river to reach their workplace in London docks and shipyards, nearly to isle of dogs.
  I was walking in the isle of dogs and wanted to reach the Greenwich side. but when I looked at
the map application on my phone, I saw no way to cross the river. But I said to myself that there must be a way to cross the river and I continued walking. Then I noticed a small circular building by the river. I went inside to see and then realized that I had found the way to cross over to the other side.