The Black Diamond ice cave is located at the Breidamerkurjökull in Iceland. Due to ash encapsulated in the ice the cave looks black. But when the sunlight shines right into the cave (e.g. early February at around 10 am) it lights up in golden and blue.
The shot was taken with 1/4 sec, f/11 at ISO 100 and 26mm focal length. Luckily no one else was in the cave!
BTW: To get to the cave you need a guide who knows the area well as the glacier is changing all the time. Siggi from http://southeasticeland.is/ was my guide: Great guy and heavily recommended!