If it was a castle, it was the strangest one he had ever seen.
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. Looking down within one saw a huge, nearly perfect bowl-shaped chamber with a single slender tower in the center. Taller than anything he had seen outside of Stoneholt, the spire looked fragile and was topped by a glassed-in chamber.
That in itself was unusual, for panes of such size would fetch a king's ransom if they could be brought down safely. The spire appeared very smooth so climbing it would be a difficult undertaking - the most obvious approach - removing them from inside - appeared to be the best choice.
This structure was 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.
Built in a meteor crater carved smooth by indebted Giants, the tower stands nearly 200' high and the top is at the focus of the dish. Around the dish were mounted a great array of reflectors fashioned with crystal, bronze and eventually spellfire crafted glass. After the assassinaton of Aardwal the tower came into the possession of a series of warlords, including Thansaal the Toarch. Thansaal used the tower for a different purpose, the incineration of undesirables. It was during his reign that the common phrase - pray for clouds - came to be used - equivilent to 'good luck' . Unfortunately for many, Thansaal's reign was marked by many beautiful summers.
Thansaal ended up slain in his own tower, though slowly. During the battle that ended his reign, many of the hundreds of mirrored reflectors were looted, reducing the towers power greatly. This did not prevent his slow, roasting death in the tower. True Death, however was denied him, for many of the spirits of his victims tormented him in his death throws and contributed bits of their essence to bind him to his corpse. The tower is still somewhat functional if the remaining glass reflectors are excavated and cleaned. It is also the dwelling place of Smoke Spirits - the remains of Thansaal's victims. Although slain by the concentrated sunfire, they retained some of its essence and are very dangerous. Thansaal himself has arisen as a charred warrior visibly past his prime in life. Although not physically impressive, he can draw upon the energies that burned him and strike out. Thansaal can be freed, should the PCs choose to, by trapping him within the focus and restoring the place to full power. This would require recovery or replacement of a large number of large reflectors. It may also be possible to create reflectors of pure magic with the correct magical research. Aardwal was close to such prior to his demise and a wizard could carry on his research to complete the spell. The tower produces concentrated light of an 'elemental' form that can be used to power enchantments - it converts solar energy to manna.