The Lair of the Fire Witch

From the introduction:

For 6-8 characters of levels 12-13 or 4-5 characters of levels 14-15. The Lair of the Fire Witch can be discovered by adventurers 100 clicks from any civilization, deep in the scorching desert. Most intruders that far into the desert are likely to die from heat stroke or dehydration. Those who manage to cling to life in the desert may mistake it for a mirage. Native nomads won’t go closer than 20 clicks out. The nomads will not answer questions about The Lair except to say that it is a compendium of heinous evil. Those who seek The Lair of the Fire Witch are giving their souls to damnation.