In the town of Chirk, in Wales (UK, Europe), there is a little canal, that crosses the valley over an aquaduct, a beautiful remnant of the industrial revolution, some centuries ago. In the valley you cannot hide from the noise of the cars on the B50708 and B4500 main roads around Chirk. But when you step into the dark tunnel for some 450 meters, all of a sudden you are walking alongside the canal in a very silent environment. The canal is in a sunken part of the terrain, and that part is surrounded by trees. You might hear a train once and a while, but I did not hear any train passing by during the time I was there.
By the way, the walk over the aquaduct is quite nice, and it leads you to a typical old Welsh pub that is just over the English border. Not very silent, out there, but enjoyable.