The dialogue in the first two panels is loosely referencing lines from the beginning of Raiders of the Lost Ark (1981).
The rocks are the collapsed bodies of the Gargrudgen, under which miles of towns and people are buried; the capitol spires are clearly visible in the distance
Essul’s “extendable legs” are something of an inside joke, to explain his mild changes in height over the course of the strip
Essul probably gained perfect sight (which he has displayed previously) through forbidden knowledge
Karbunkel explains Yotatonic Theory and the two timelines to Cornelius
Karbunkel has met with Yotatonic people before, in #80 and #123; here we see him contacting them when he was younger than Cornelius, indicating the length of time it took for the Garblemen to arrive
By showing Cornelius a “flashback”, Karbunkel changes a memory from Perceptive to Narrative timeline (it’s out of Karbunkel’s memory, and now part of the depicted narrative)
In panel 2, young Karbunkel has a piece of Smisland spar, which is used to power his telescope (panel 1), and that’s Mogol next to him