Krafla includes one of the two best-known Víti craters of Iceland (the other is in Askja). The Icelandic word “víti” means “hell”. In former times, people often believed hell to be under volcanoes. The crater Víti has a green lake inside of it.
South of the Krafla area, but not actually within the caldera is Námafjall, a mountain, beneath which is Hverir, a geothermal area with boiling mudpools and steaming fumaroles. (Wikipedia)
An interesting fact about Iceland: the youngest country in the world
Geologically speaking, Iceland is hardly out of playschool, since it only began to rise from the North Atlantic seabed about 25 million years ago, the product of volcanic eruptions that are still going on today. Parts of the country are still so rugged that American astronauts chose Iceland as a training ground to prepare them for landing on the moon. And Iceland is still taking shape before peoples eyes: the newest land is Surtsey, an island which rose from the sea during an underwater eruption off the south coast in 1963. (http://midatlantic.icelandair.com/destination/iceland-facts/)