Valefire

Ask anyone in Kundar why their street lanterns have tubes connecting them, and they’ll tell you about the large gas deposits deep beneath the huge canyon that power small fires and heating systems throughout the city. The nights can sometimes be as cold as the days are hot, so the heating systems really help the city to thrive.
Ask anyone in Kundar why there is such incredible security (secure enough that most are not permitted to know the full extent of the measures in place) around the deposit underground, and they will simply look at you and say “the Day of Valefire.”
It is the sad fact that there used to be two large gas deposits under Kundar, and in the early days of the city being built centuries ago, when these were first discovered, the regulations around how and who had access to them were far less stringent. Incredibly, it took almost a decade before there was a full-scale disaster, when a simple cantrip by a mage inspecting the smaller cavern set the whole thing alight.
The valley erupted - a huge portion of the growing city of Kundar exploded high into the air, some massive pieces flying several miles to impact into the other side of the canyon, collapsing a number of the mines there. Fire engulfed a large part of the city, and the gas fountained out in a huge jet of flame for days until it was finally depleted. This titanic flame was dubbed ‘Valefire’ or ‘Tiamat’s Breath’ or ‘Bahamut’s Breath’ depending on your religious persuasion. People couldn’t even approach it without being burned from a hundred feet away. When it eventually went out, that portion of the city was vaporised - nothing remained.
The years have passed and the hole was eventually filled and built over, the mines reopened and the security of the remaining gas pocket increased dramatically, to ensure this incredible disaster can never occur again.