Nanobridges with widths down to 140 nm and lengths of about 250 nm were structured in a 25 nm YBa2Cu3O7-δ thin film, by means of a substrate-etching technique. At low temperatures, the current-voltage characteristics of these bridges show clear signs of periodic single-vortex motion. A quantitative comparison could be made with a vortex-flow model, which descirbes the forces acting on the vortices inside a hyperbolically shaped nanobridge, with dimensions much smaller than the thin film magnetic-penetration depth. It follows that the related viscous drag coefficient η is approximately 1.0×10-10kg/ms and the penetration depth is approximately 4 μm. These values indicate that the transport properties are dominated by the weak-link behaviour of grain boundaries or twin boundaries in the thin film.