Superfluid helium supports well-defined vortices with quantized circulation. Despite the quantization, vortex behavior obeys the same rules governing classical vortices -- with simplifications, since quantization forbids many of the motions allowed in the classical case. We study a single quantized vortex stretched between a wire and the wall of a cylindrical container, with a measurement technique that allows tracking of single vortex motion. I will describe some of the characteristic behaviors we observe, which follow simple principles of hydrodynamics. I will emphasize our excitation and observation of vortex oscillations first predicted by Lord Kelvin, including recent measurements suggesting a transition to a non-linear regime. These oscillations are thought to play a key role in low-temperature superfluid turbulence.