  So-called "regular black holes" are a topic currently of considerable
interest in the general relativity and astrophysics communities. Herein we
investigate a particularly interesting regular black hole spacetime described
by the line element \[
ds^{2}=-\left(1-\frac{2m}{\sqrt{r^{2}+a^{2}}}\right)dt^{2}+\frac{dr^{2}}{1-\frac{2m}{\sqrt{r^{2}+a^{2}}}}
+\left(r^{2}+a^{2}\right)\left(d\theta^{2}+\sin^{2}\theta \;d\phi^{2}\right).
\] This spacetime neatly interpolates between the standard Schwarzschild black
hole and the Morris-Thorne traversable wormhole; at intermediate stages passing
through a black-bounce (into a future incarnation of the universe), an extremal
null-bounce (into a future incarnation of the universe), and a traversable
wormhole. As long as the parameter $a$ is non-zero the geometry is everywhere
regular, so one has a somewhat unusual form of "regular black hole", where the
"origin" $r=0$ can be either spacelike, null, or timelike. Thus this spacetime
generalizes and broadens the class of "regular black holes" beyond those
usually considered.
