The normal climb starts in Arsiero (308m) (or just above (361m) if coming from Passo Xomo (1059m)) and goes via Tonezza (and Sella (1110m)) after which you come to the turn-off for the Vena road. You can take this minor road and climb via Passo di Vena di Sotto (1496m) and Passo di Vena di Sopra (1545m) to meet the main road again just before the turn-off for Valico di Valbona (1781m). This pass is at the tunnel at the start on this road. You can also skip the Vena road and take the main road of course.

Most fun and for a more consistently steep climb you should take the small road from Barcarola (303m), which has no sign-posts, but there is only that road going up here. It has 24 numbered hairpins and seems like it is only used by the occassional cyclist. You come up the main road just as you approach Tonezza.