am training at mo myself for marathon in october. The run i do is a loop but it's quite good as each loop is 6.5 miles . starting from goose green, then east dulwich grove, dulwich village, up college road to the top of the sydenham hill, then run down sydenham hill towards the horniman , along wood vale then down to peckham rye. its a bit better than doing loops of dulwich park but again thats good because its a 1 mile loop. hope that helps