If you are coming from T-centralen take the front exit (Ringvägen) and go out to the left after the gates. Follow half arrows to the start at Small Blecktornsparken.
There will be a runner's trail (around 6-7 km'ish), and a walker's trail (maps will be provided). The trail is mostly bike-friedly (with some exceptions).
On-inn will be Söder Bar & Restaurang (Ringvägen 125, by the Skanstull Tunnelbana), no pre-orders necessary.