  We study aspects of the extended gravitational thermodynamics for the
Taub-NUT and Taub-Bolt geometries in four dimensional locally anti-de Sitter
spacetime, where the cosmological constant is treated as a dynamical pressure.
Attention is paid to the phase structure in the (p,T) plane, which has a line
of first order phase transitions extending from the origin. We argue for a
dynamical interpretation of the unstable physics in the negative specific heat
region. A deformation corresponding to a dyonic Taub-NUT/Bolt system is also
explored, and the effect of the deformation on the phase diagram is
characterised.
