Could you explain why the following articles are used as they are used...
If you get the (why is A not used here) chance to visit London you really should take the time to visit Greenwich. You can get there by train, bus, taxi or even walk if you have the (why do we need an article here, energy is uncountable, shouldn't we leave it blank?) energy. Personally, though I recommend taking a boat. The one I took was from (why don't we use THE here but put it in the next case) Tower Bridge, which is next to the Tower of London.
My comments are in brackets.