From the Drau bridge in Lavamünd, hike north on the eastern bank, cross a road and continue along a hiking trail uphill past the farms vlg. Rachur and Waldegger farms and some very beautiful wayside crosses in about one and a half hours to the Ruskreuz (starting point of the geological nature trail, path "306,03").
Continue in the same direction over a forest ridge to the Rottensteiner Kreuz. Here it goes a good ten minutes over a hollow way slightly uphill to the intersection Ruine Rabenstein / Gasthof Rabensteiner or Kasparstein / Eiser Törl. Turn right here, along hiking trail 306A, past the farmstead vlg. Weißegger farmstead. It is still a 20-minute walk to Gasthof Rabensteiner.
Since this stage is short, you still have enough time to hike from Gasthof Rabensteiner along trail 306A below the castle ruins to St. Paul and its famous Benedictine monastery - it's worth it (additional time there and back about 1 hour 45 minutes)!