I know this has been discussed before but I can't find the thread. It is by way of being a Public Service Announcement.
Mr fimm, a friend and I came through the new(ish) Royal Infirmary of Edinburgh path to get from Morningside to Myreside Road. When we got to the new path we noticed that the route back towards Morningside, which has always been blocked off in the past, was open. So we went to have a look.
It is just a muddy and potholed track at the moment, and it brings you out on the lawn in front of a building; if you cycle across the grass you end up at a steepish little slope and then you come out on a road which I think must be Morningside Terrace.
We just turned round and went back. I can see them (Mr fimm and Friend Of Mr fimm) using it when they are on their mountain bikes (as we were last night).