  Large, localized variations of light scalar fields tend to collapse into
black holes, dynamically "censoring" distant points in field space. We show
that in some cases, large scalar excursions in asymptotically flat spacetimes
can be UV-completed by smooth Kaluza-Klein bubble geometries, appearing to
circumvent 4d censorship arguments. However, these spacetimes also exhibit
classical instabilities related to the collapse or expansion of a bubble of
nothing, providing a different censorship mechanism. We show that the Kerr
family of static KK bubbles, which gives rise to an infinite scalar excursion
upon dimensional reduction, is classically unstable. We construct a family of
initial data in which the static bubbles sit at a local maximum of the energy,
and we give a general argument that such a property indeed indicates mechanical
instability in gravity. We also discuss the behavior of wound strings near a
bubble, a local probe of the large traversal through moduli space.
