The Ciclovia Alpe Adria [bike route from Alps to Adriatic] is a joint Austrian-Italian project to connect, as the name suggests, the Austrian Alps to the Adriatic Sea; to be more precise, the route starts at Salzburg and ends at Grado.
Currently (2011) there exist dedicated bike paths only in some places; in other locations work is nearing completion.
In the section between Tarvisio and Gemona part of the bike path follows the route of the former Pontebbana Railway, which had run on a single track until it was decommissioned early in this century and replaced with a new double-track alignment that runs mostly through tunnels, a solution more appropriate for the Venezia-Vienna line.
Here are some possible trip segments of this larger route:
and two related routes that cross the border into Slovenia