From A Wiki of Ice and Fire
and the location of the Brimstone
The Brimstone is a river in southern Dorne, known for its sulphurous waters. The Hellholt, the seat of House Uller, sits next to the river.
House Dryland ruled as Kings of the Brimstone from Hellgate Hall until the last of their line, Lucifer Dryland, was sent to the Wall by Nymeria.
References and Notes