NorthernEurope

Due to its position on the Mid-Atlantic ridge, Iceland is one of the most active volcanic regions in the world. Its unique geological conditions make for some awe-inspiring rock formations, both beneath the surface as well as above it. Various tube caves—formed by magma flowing underneath the earth's surface after lava has solidified overhead—can safely be explored through guided excursions year-round. For safety reasons, different caves are explored during different seasons. The most commonly visited caves are the Gjábakkahellir Cave near Þingvellir National Park in the summer months, and the Leiðarendi Cave in the Bláfjöll area in wintertime. https://www.inspiredbyiceland.com/things-to-do/activities/caving/

The world's largest limestone mine. An endless maze of galleries with caves as large as cathedrals and narrow paths where an adult man cannot walk upright. An enormous 60 km labyrinth of passageways with caverns as large as a cathedral, and narrow tunnels where you have to walk doubled up. 2 km of the passageways are lit. A multi-media presentation shows the history of the mines. Exhibitions and films tell about bats, geology and mining. Groups are granted admission all the year round with prior reservation. Guided tours in Danish, English and German can be arranged. https://www.visitviborg.com/viborg/plan-your-trip/monsted-limestone-mines-gdk601327