The Big Picture by The Boston Globe has a great series of photographs of scientists and crazy adrenaline junkies descending into Nyiragongo Crater. Go see it here:
Nyiragongo Crater: Journey to the Center of the World
Rapelling down over 1,000 feet into the crater is incredibly risky. Not only does one risk death from falling rocks and the highly unstable volcanic slopes with chemically-rotted volcanic rocks and frequent tremors, there is the risk of asphyxiation from carbon or sulfur dioxide, and the risk of even a small amount of lava "burping" out and spilling over the crater rim.
This is one of my favorite pictures from the set.
The Eye of Hell. Below is a time-lapse video of the Nyiragongo lava lake from another source. In this video, 1 second of video time is equal to 1 minute of real time.
This video makes me think of the earliest Earth, four and a half billion years ago, still mostly molten with a thin "scum" crust forming and reforming and moving around in a frenetic type of plate tectonics. It seems like it would be a neat place to visit and see (which will never happen).