  In this work we characterize all the static and spherically symmetric vacuum
solutions in $f(R)$ gravity when the principal null directions of the Weyl
tensor are non-expanding. In contrast to General Relativity, we show that the
Nariai spacetime is not the only solution of this type when general $f(R)$
theories are considered. In particular, we find four different solutions for
the non-constant Ricci scalar case, all of them corresponding to the same
theory, given by $f(R) = r_0^{-1}\left\lvert R-3/r_0^2\right\rvert^{1/2}$,
where $r_0$ is a non-null constant. Finally, we briefly present some geometric
properties of these solutions.
