Deeping Steppes as named by Dargain the Gnomish adventurer who happened upon this place when attempting to find lost friends in a nearby series of caves and was swept in by the unexpected surge of an underground river, perhaps due to shifting of plates or erosion of a natural barrier. The cavern was sealed and unknown until being discovered by Dargain.
This is a region of the underdark where a series of very large plateaus occupy a huge underground cavern. The cavern is situated near a very common and sometimes treacherous underdark route know as The Underway (in my version of the world) which reaches from the Dales to Silverymoon regions in the Forgotten Realms.
The Nomin gypsies have a fiddling competition every year, known as the Danse de Velose. Beaters hit out the rhythm on taut drums and the competitors start to play, slowly at first. Youngsters can compete, but are soon pulled away by worried mothers, before the competition becomes too dangerous. After two hours the haunting tune has become dazzlingly fast. You can resign at any time, but the moment you make a mistake you receive an arrow through the neck. Strings may snap, but the players must play on. The whole affair never lasts much longer than three hours, and the last fiddler playing is crowned king of the gypsies.