Here's a short little evening route I sometime do. It's pretty good.
Without leaving the city of Edinburgh, it's a bit of bike paths, plenty of off-road walking paths with a little bit of quiet roads.
It takes you over Craigmillar hill with it's fun little paths, through Insh Park, up to and through the lovely woods of Mortonhall, back over the top of the Braid hills. Then there's a nice run down the upper sections of the Hermitage of Braid to finish the offroad sections.