New Zealand artist Chris Booth creates magnificent and seemingly impossible sculptures using rocks, boulders, wood, and other natural items. This one is called "Cave":
Cave, entranceway to the Kati Kuri marae at Kaikoura, comprises 5000 white limestone pebbles, collected with community assistance from the coast and woven into a helix. Built around a wooden former then erected into position by crane, the ‘skin’ of pebbles is attached to the stone arcs at each end. Many important events have taken place at this marae, including the final signing of land settlements between representatives of Kai Tahu and the government after 200 years of grievances and injustices since colonisation. The late Upoko Wiremu Solomon and his wife Reo led the revitalisation of the marae and its buildings for the community. He also led the establishment of the now famous Whalewatch tourist venture, which ploughs funds back into the community.
Link - via Ursi's Blog