The Big Picture at Boston.com has a fascinating series of photographs of an expedition to the Nyiragongo Crater in central Africa. The few examples reproduced here are much reduced in size.
Until this expedition, no-one had survived standing on the rim of the boiling lake of lava in the center of the volcano's crater. Members had to take with them protective gear to withstand the 1,300 degree temperatures on the rim.
The 282 million cubic feet of lava is never still. Note the team member (circled in yellow) standing at the foot of the rim wall. He had to be constantly in touch by radio with other team members, who would warn him if the wind changed direction, risking sending choking fumes or lava flows towards him.
The lava inside the crater is constantly boiling and bubbling due to subterranean eruptions of gas and magma that bubble up from below. It's been compared to the sea. Here's a video clip of the lava lake, taken at night, which shows the waves that form on the lava's surface.
There are many more photographs at the link, all considerably larger than those I've reproduced here. They make fascinating and highly recommended viewing.