  We fully describe the horofunction boundary $\partial_h L_2$ with the word
metric associated with the generating set $\{t,at\}$ (i.e the metric arising in
the Diestel-Leader graph $\text{DL}(2,2)$). The visual boundary
$\partial_\infty L_2$ with this metric is a subset of $\partial_h L_2$.
Although $\partial_\infty L_2$ does not embed continuously in $\partial_h L_2$,
it naturally splits into two subspaces, each of which is a punctured Cantor set
and does embed continuously. The height function on $\text{DL}(2,2)$ provides a
natural stratification of $\partial_h L_2$, in which countably-many
non-Busemann points interpolate between the two halves of $\partial_\infty
L_2$. Furthermore, the height function and its negation are themselves
non-Busemann horofunctions in $\partial_h L_2$ and are global fixed points of
the action of $L_2$.
