From 9th-century Norse pagans to 21st-century followers of Björk’s pagan poetry, adventurous types have long flocked to Iceland. The terrain is a destination all its own—expanses of nubby, black lava ...

Giant's Causeway in Northern Ireland features around 40,000 exposed polygonal columns of basalt in perfect horizontal sections. Chris Hill/Photodisc via Getty Images The reason patterns often appear ...