The 5 is a trail that crosses the Northen slopes of Immitos from east to west or from west to east (depends from were you heading i guess) and passes nearby the characteristic antenna building of OTE at the last turn before the entrance of the infamous 10 trail.
Thus most of the riders that use it preffer to consider as a starting point this building.
From that building and exactry on the turn of the tarmak road, just dive into the weastern entrance. You'll find yourself descending through a trail on the western slop under the korakovouni area. You'll find lots of loose stones, in comparison to the same trail of the eastern slopes.
The trail crosses the dirtroad that circles the western slopes of Immitos.
The trail goes on after crossing the dirtroad and gradually reaches Anthousa tower. From there you may go on & descend toewards the bridges at the base of kessariani area, throught the Vrahovraho trail....