The Path
The Number 1 National Cycle Route uses this path - from the start at Roseburn and taking the Silverknowes route off to the left a little over a mile along. The path starts on Russell Road in Gorgie, not far from Tynecastle - the entrance is not immediately obvious being just where there is a 90 degree bend in the road and pavement. The section of pavement heading to/from Gorgie is shared with pedestrians. There are a number of information boards along the path, unfortunately most of these have been vandalised. The path is quite heavily used by both pedestrians (many walking dogs) and cyclists, so care and courtesy is required. The surface is for the most part good, although tree roots make it bumpy in places. In the past there always seemed to be a fair bit of broken glass on it, but that seems to have reduced over the last little while. I used to use this route most days on my way to and from South Queensferry - it's certainly less frightening than Queensferry Road!
There is a short, sharp uphill at the very start before it levels out. A short distance along is an old station. There are many on and off points for this path - some of them have steps that require carrying your bike if you wish to use them - including a link to the Water of Leith that runs below (which I don't recommend.)
Being an old railway, the gradient is pretty flat, although it's slightly downhill most of the way to Leith and therefore uphill on the way back.
A little over a mile along is a junction with a sign towards South Queensferry. Beware other cyclists emerging from here without stopping (or looking.) This goes up past Drylaw to Silverknowes and Davidsons Mains. The main route continues on for another 3 or so miles, with various turn offs, passing Trinity, Victoria Park and eventually coming out at Leith, not far from Ocean Terminal (turn left at the end to get there - although beware - this road can be very busy.)
The Pedal for Scotland route from Glasgow to Edinburgh usually uses this path for the last stage, picking it up at Silverknowes and ending at Victoria Park.
The second phase of the Edinburgh Trams project is supposed to take part of this route. There has been quite a lot of concern that the plans, although supposed to include provision for cyclists, may not leave a wide enough path to do so. At the current rate of progress however, I suspect that this section will never be built.