  We investigate properties of the inner horizons of certain black holes in
higher-derivative three-dimensional gravity theories. We focus on BTZ and
Spacelike Warped Anti-de Sitter black holes, as well as on asymptotically
Warped de-Sitter solutions exhibiting both a cosmological and a black hole
horizon. We verify that a First Law is satisfied at the Inner horizon, in
agreement with the proposal of \cite{Castro:2012av}. We then show that, in
Topologically Massive Gravity, the product of the areas of the inner and outer
horizons fails to be independent on the mass, and trace this to the
diffeomorphism anomaly of the theory.
