A City on the Sun

From publisher blurb:

Mini-Dungeon adventure for 5 characters of level 18

A grief-stricken wizard's apprentice began raving that the sun itself had to be extinguished.

Now, several cities across the globe have been consumed by beams of focused light that astronomers confirm originate from the planet’s sun.

As inhabitants of other metropolises evacuate, the party heads to speak to the apprentice in an attempt to prevent further calamity.