Bláfjöll are located around 20 km from Reykjavik, by the lava plateau of Hellisheidi. The mountains are the most popular skiing venue for the people of Reykjavik and its surroundings. The area is strong with volcanic activity, with frequent earthquakes and the lava that became Kristnitokuhraun lava field flowed from there in the year 1000. Kristnitokuhraun is located at the outskirts of the Blue Mountains. Also in the area is the fascinating underworld of the lava tubes.
The lava field Kristnitökuhraun is formed during an eruption in the year 1000, when Icelanders were debating the christening of the nation at national parliament Alþingi at Þingvellir. The story goes that when the eruption started, believers in the old gods claimed that was a token of the wrath of the gods, to which chieftain Snorri Goði is said to have responded "So what were the gods angry about when the lava flowed that we are now standing on?"
Hengill volcano is still active, evidenced by its numerous hot springs and fumaroles, but the last eruption occurred approximately 2,000 years ago.
The volcano is an important source of energy for the south of the country, which is captured at the Nesjavellir power station and the Hellisheiði power station. Both stations are operated by Orkuveita Reykjavíkur (Reykjavik Energy).
The area with its mountains and hot springs is well suited for hiking and there are a lot of hiking trails. The small town of Hveragerði with its multitude of hot springs is also part of the Hengill area.
Some folk tales and sagas are connected to the region. For example, a young farmer is said to have killed the sleeping troll woman Jóra while she lay in wait for innocent wanderers or horsemen on the trail over Dyrafjöll.