A route for the most part on unpaved, gravel bike paths, and between Portegrandi and Caposile on a footpath suitable for mountain bikes; the route starts at Quarto d’Altino, follows the river Sile, and then, hugging the lagoon [Lagoon of Venice], follows the route of the Piave Vecchio [former alignment of the Piave River] and ends up at San Donà di Piave (or vice versa).
Point of departure is the train station at Quarto d’Altino; after you emerge from the sottopassaggio [underpass] next to the Hotel Crown Plaza, turn left and you will come upon the bike path; after a few hundred meters/yards, cross the road and a bit further you will find on the right Via Claudia Augusta, which here is a long straight run towards Altino; but before coming to Altino you are forced to turn right onto a bike/pedestrian path along the river Zero, it is unpaved [gravel] but bike-able (in fact, one can see traces of asphalt here and there.)
The bike path follows the tortuous route of the river Zero, up to where you get back on the road to (*)Altino; where they come together you will be in the middle of the excavation sites in front of the new Museo Archeologico of Altino; from here head north and after a short distance on the left you will come to a piazzale with a church and the actual Museo Archeologico on the right, which definitely is worth a visit (tickets cost 2 euros). There are many archeological finds from this ancient Roman city: funerary urns and headstones, glass and everyday objects.
After Altino there is a long straight section that is paved and ends at the lungosile [“along the Sile”]; here next to the paved road there is an unpaved bike/pedestrian path that follows the bends of the Sile up to Portegrandi, where you arrive at the lagoon. There is a drawbridge that takes one to a small shipyard and marina. Once past this bridge you end up on a white gravel road that runs for a couple of kilometers [about 1.4 miles] keeping the lagoon on the right and the final section of the Sile to the left.
Once you are past the last houses, the roughest segment of this route begins: the white road becomes yellow green in the sense that it is reduced to a single footpath cut in the grass; after a short distance the path drops down to the level of the water (at very high tide you may have to wade through!), goes through the salt marshes and then rises up again; the route continues on the grass pavement, rather uneven, but acceptably bike-able; for those who are not used to mountain bike trails (me, for example) you can’t help but doing some of the trail on foot. Continue on between the Sile and the lagoon, where the water now seems interwoven with the salt marshes; were it not for the distant noise that comes from the road traffic on the other side of the Sile, you might think you are in a wilderness far away from so-called civilization.
At last you return to the white [gravel] road and then to a paved section that takes you to a pontoon bridge over the Sile; here one can decide: continue without crossing the bridge and you will travel on a paved road that follows between the Sile and the lagoon as far as Jesolo Lido; it is a narrow road and peaceful in the winter, but less tranquil during the summer when unfortunately the race to get to the beaches virtually precludes this route.
Alternatively, cross the pontoon bridge, turn a sharp right onto a small road that after a short distance comes to a drawbridge this time over the Piave Vecchio. The bridge is open only to bikers and pedestrians; once over the bridge turn left onto a paved road, after you cross the very busy road (SP 43) take the road north that starts right there (Via Chiesanuova) and that runs along the east side of the Piave Vecchio. This section is paved and narrow but with little traffic and follows the Piave as far as Chiesanuova and then to Musile di Piave; here towards the right we come to a bridge with a bike lane on the right side, and immediately after you come upon the town of San Donà di Piave, where there is an FS train station on the Venezia-Trieste line.
