I recommend the following book:[https://www.amazon.co.uk/Scottish-Trail-Running-Great-Runs/dp/1906095396](https://www.amazon.co.uk/Scottish-Trail-Running-Great-Runs/dp/1906095396)
There are good ideas within driving distance of Glasgow (many of which are mentioned in this thread already)
This is decent for ideas as well:[https://www.plotaroute.com/routes/running/popular/1?RouteID=&RouteName=&Locality=Glasgow&CCode=&MinDist=8&MaxDist=&MaxAscent=&Terrain=Any](https://www.plotaroute.com/routes/running/popular/1?RouteID=&RouteName=&Locality=Glasgow&CCode=&MinDist=8&MaxDist=&MaxAscent=&Terrain=Any) |