From Fallen London Wiki

For what it's worth, when I followed the guide earlier (before seeing these comments - I just came back to double check the last option), I saw "In the Mirror Marches" and assumed/understood that it meant I'd have to get there myself, so I don't think it was that obtuse. However, I've edited the Medium section to be more clear that it requires the usual way of entering the Mirror Marches, just so it's more clear in the future.