“ If it was a castle, it was the strangest one he had ever seen.
He of course saw the main tower - taller than anything he had seen outside of Stoneholt, the spire looked fragile and was topped by a glassed-in chamber.
The outer wall was so gently sloped that it would have only stopped a horde of hobbling old men, an able-bodied soldier could stride up to its crest with little effort. Within one saw a huge, nearly perfect bowl-shaped area with the base of the tower in the centre, covered in hundreds of mirrors.
----
This structure is a massive solar collector designed by the Wizard-King Aardwal in centuries past. He used the concentrated light in his investigations into the magic of light, and in the fashioning of flash crystals.”
“ A small, primitive village has yet to discover fire, which is a good thing because there are highly flammable (but not otherwise dangerous) gasses in the air. The heroes, blissful in their ignorance, don't know that and think it a wonderful idea to show the locals open flame.”