  We present measurements of how a single vortex line in superfluid helium
interacts with a macroscopic bump on the chamber wall. At a general level our
measurements confirm computational work on vortex pinning by a hemispherical
bump, but not all the details agree. Rather than observing a unique pin
location, we find that a given applied velocity field can support pinning at
multiple sites along the bump, both near its apex and near its edge. We also
find that pinning is less favorable than expected. A vortex can pass near or
even traverse the bump itself with or without pinning, depending on its path of
approach to the bump.
