Cheers - what I've got worked out so far is along to Arthur's Seat (at 12 o'clock, if you see what I mean), round it clockwise until you get to a roundabout at about 7 o'clock, then almost back on yourself, round Duddingston Loch, down to Craigmillar castle, then back up the A7 to the sam roundabout (th 7 o'clock one), then round the rest of Arthur's Seat, then back the way you've come - that looks like about 10 miles.
How does that sound?