National Geographic explorers venture into the most prohibitive places on Earth. In this gallery, check out some epic moments from recent expeditions, including a team of scientists who journeyed into the caldera of the Nyiragongo volcano located in the Democratic Republic of Congo (pictured here). "Down here you feel the volcano," says photographer Carsten Peter. "It's a low-frequency rumbling that pulses through your body—like being inside a giant subwoofer." —Natasha Daly