Is the following sentence syntactically correct?
Standing on the edge of Red Square with its colourfully painted domes it [St Basil's Cathedral] is the most famous image of Russia.
You don't use articles with names of squares, do you?
If I were a native speaker of English, I would never shut up. :-)
We don't use "never" or "always" on the forum because of the number of exceptions but in the example you gave, you're right, it's just "Red Square".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.