Ruins of the Roslin Glen Gunpowder Mill should be added. See also http://www.secretscotland.org.uk/index.php/Secrets/RoslinGlenGunpowderMill
On the satellite images the buildings are not visible under the trees, so it needs surveying on the ground.

Should this be a path in OSM? You can walk over the grass but I couldn't see any sign of a track or trampled-down grass that people actually do that. It looks just like an ordinary patch of grass.

This looks like a 3-dimensional drawing of the building, not a map.

The corridor through RIE is marked as a footpath. This is a bit awkward as it isn't really a path, although you can of course walk through. What's the correct tag for this situation?

It also didn't specify whether cycling and horse riding is allowed, so I changed that at least.

Old Homebase building has been removed, new (BHS?) looks almost finished. New bike racks already installed but currently behind a building fence.

These bike racks are being replaced with 2-level racks and much more capacity - installation still ongoing, should be updated when finished.

New bike racks at Gilmerton Crossroads