Sadly, while the Real Mary King's Close tour is the only way to visit that particular historic close -- and as I have described in the last post the tour makes some troubles with not permitting photographs -- I might have something even better to offer: photos from a very, very similar close nearby, and which is NOT bricked over the way that Mary King's is.
Behold: Byres' Close.
It is named for Sir John Byres, who lived ca. 1569 - 1629. The location is on the same block and was built around the same time as Mary King's. The deep slope and step pattern is almost identical to that found in Mary King's and the buildings are of a similar appearance.
It's of note that while the actual sign over the close reads "Byres' Close" some sources say "Byre's Close" or "Byres's Close" or just "Byres Close."
Just about the only difference between Byres' and Mary King's is that Byres' Close is just a little more narrow -- I think maybe about a foot less wide than the preserved section of Mary King's. Mary King's also has fewer steps in the preserved section, being mostly slopes.
I am told Mary King's would not originally have been paved -- I assume neither would Byres'. But one can clearly see that these cobblestones are not exactly new. I think "originally" may be a relative term; perhaps it was raw dirt in the 1500s when it was new but probably by the 19th century it looks like it would have been paved.
Surrounding buildings in Byres' are still inhabited -- in fact, while taking these pictures I met a nice fellow who was out for a smoking break, and a whole family filing through in a row, all carrying suitcases, apparently lodging in the area. Some sources (like the city of Edinburgh's own website!) claim Byres' Close is not open to the public, but that seems to be a mistake, as there are definitely businesses operating in there -- (perhaps they only open for limited hours?)
Having seen Mary King's I can say that this nearby place is so similar in appearance that if you just hung some fake clotheslines overhead, one would probably not be able to tell the difference between the two in a photo -- I could not say this of other nearby closes like Craig's Close or Anchor Close. And once again, Byres' Close has the benefit of still having the rooftops open, so it is actually more similar to its historical appearance than modern Mary King's would be.
However, if you must see documentation of the real thing, some older pictures from Mary King's Close and buildings are available at this website.