It should have been:
"For a visitor to London, it..."
As a visitor to London, you'll find it the most reliable and quickest way toget from one place to another.
This is grammatically correct, but changes the style of the paragraph, as the sentence is personally addressing the reader.
When a visitor visits London, it is the most reliable and quickest way to get from one place to another.
With the change to singular verb, it is grammatically correct, but suffers the drawback of repetition: 'visitor visits'.
'go' means to 'move from one place to another'.
'get' combines this with the sense that there is some difficulty involved e.g.
"How can I get to the airport from here?"
"I finally got there."
Hence, "it is the most reliable and quickest way to get from..." that is, presenting the least time-consuming, and with fewest difficulties, way of reaching your destination.