  We analyze null- and spacelike radial geodesics in Schwarzschild-de Sitter
spacetime connecting two conjugate static sphere observers, i.e. free-falling
observers at a fixed radius in between the two horizons. We explicitly
determine the changes in the causal structure with respect to these natural
observers as a result of the inward bending of the black hole singularity, as
well as the outward bending of asymptotic infinity. Notably, the inward and
outward bending changes as a function of the black hole mass, first increasing
towards a maximum and then decreasing to vanish in the extreme Nariai limit.
For a generic mass of the black hole this implies the existence of finite size
(temporal) windows for the presence of symmetric radial geodesics between the
static sphere observers probing the interior region of the black hole, as well
as the exterior de Sitter region. We determine the size of the interior (black
hole) and exterior (de Sitter) temporal windows in $4$, $5$ and $6$ spacetime
dimensions, finding that they are equal in $D=5$, and compute the proper
lengths of the symmetric radial geodesics. We comment on the implications for
information exchange and the potential role of the symmetric radial geodesics
in a geodesic approximation of static sphere correlators in Schwarzschild-de
Sitter spacetime.
