Michele Westmorland / Schooling fish around healthy reef system, Castle Rock, Komodo National Park, Indonesia.

Carol Walker / Purebred black Friesian stallion being trained to perform the 'spanish walk', Castle Rock, Colorado, USA Model released

Tim Fitzharris / Castle Rock overlooking Lake Superior, Pictured Rocks National Lakeshore, Michigan

Juan Carlos Munoz / View across fields and drystone walls to O'Brien's Castle. Inisheer, Aran Islands, County Galway, Republic of Ireland. May 2011.

Marie Lochman / Castle Rock, Porongurup National Park, south west, Western Australia, March 2012

Ernie Janes / Tantallon Castle, East Lothian, on the Firth of Forth, with Bass Rock and the Gannet (Morus bassanus) colony, in distance, UK, July 2018.

Jeff Foott / Rock formation in winter, The Castle, Capitol Reef National Park, Utah

Jeff Foott / Rock formation in winter, The Castle, Capitol Reef National Park, Utah

Jeff Foott / Rock formation, The Castle, Capitol Reef National Park, Utah

Ashley Cooper / La Calahorra Castle in La Calahorra at the foot of the Sierra Nevada mountains in Andalucia, Spain,

Ashley Cooper / La Calahorra Castle in La Calahorra with spring flowers, at the foot of the Sierra Nevada mountains in Andalucia, Spain.

Nick Upton / Ancient stone staircase with 913 steps zigzagging up to Palamidi Castle, a Venetian fortress on a hill overlooking Nafplio and the Argolic Gulf, Argolis, Peloponnese, Greece, July.

Ernie Janes / Tantallon Castle and the Bass Rock, East Lothian, Scotland, UK, June 2017.

Tim Fitzharris / Mesa, Castle Rock, Castle Valley near Moab, Utah

Graham Eaton / A dry valley, cut through carboniferous limestone in Cave Dale and Peveril Castle, Castleton, Derbyshire, UK November

Kevin Schafer / Mesa in winter Castle Valley, Utah

Franco Banfi / Rocca di Calascio, a 13th century castle in the mountains, Aquila, Abruzzo, Italy, May 2006.

Colin Monteath / Limestone boulders with snowfall, Craigieburn Range, Castle Hill Basin, Canterbury, New Zealand

Colin Monteath / Limestone boulders in field, Craigieburn Range, Castle Hill Basin, Canterbury, New Zealand

RHONDA KLEVANSKY / Giants castle mountain rock face in orange light, Drakensberg, Kwazulu Natal, South Africa, July 2009.

Ross Hoddinott / Bench in front of a wall with Lindisfarne Castle in the distance, Holy Island, Northumberland, UK, April 2013.

Ross Hoddinott / Round rocks on beach with Dunstanburgh Castlle in the distance, Northumberland, UK, April 2013.

Ross Hoddinott / Bamburgh Castle, early morning light at dawn, Bamburgh, Northumberland, UK, April 2013.

Nick Upton / Sarsen stone megalith on the Ridgeway near Barbury Castle, Marlborough Downs, Wiltshire, UK, May.

Nick Upton / Sarsen stone megalith on the Ridgeway near Barbury Castle, Marlborough Downs, Wiltshire, UK, May.

Gavin Hellier / The Rock Castle of Uchisar, Cappadocia, Anatolia, Turkey, 2008

Gavin Hellier / Old troglodytic cave dwellings and the rock Castle of Uchisar, Cappadocia, Anatolia, Turkey, 2008

Gavin Hellier / Old troglodytic cave dwellings and the rock Castle of Uchisar, Cappadocia, Anatolia, Turkey, 2008

Carol Walker / Andalusian horse (ancient spanish breed), mare raising foreleg, performing dressage steps without a rider, Castle Rock, Colorado, USA, 2011

Carol Walker / Andalusian horse (ancient spanish breed), mare performing dressage steps without a rider, Castle Rock, Colorado, USA, 2011

Carol Walker / Trakehner horse (ancient prussian breed), mare performing dressage steps without a rider, Castle Rock, Colorado, USA, 2011

Carol Walker / Trakehner horse (ancient prussian breed), mare performing dressage steps without a rider, Castle Rock, Colorado, USA, 2011

Vincent Grafhorst / Familiar Chat (Cercomela familiaris) on a rock, Giant's Castle Nature Reserve, South Africa

Vincent Grafhorst / Augur Buzzard (Buteo rufofuscus) landing on a rock, Giant's Castle Nature Reserve, South Africa

Vincent Grafhorst / Bushman rock paintings in the Drakensberg Mountains, Giant's Castle Nature Reserve, South Africa

Vincent Grafhorst / Bushman rock paintings in the Drakensberg Mountains, Giant's Castle Nature Reserve, South Africa

Colin Monteath / Boulders of Prebble Hill with Torlesse Range behind, Castle Hill Basin, Canterbury, New Zealand

Philip Dalton / Castle ruins and Lighthouse on Bass Rock in the Firth of Forth, East Lothian, Scotland, UK

Philip Dalton / Castle ruins and Lighthouse on Bass Rock in the Firth of Forth, East Lothian, Scotland, UK

Alan Watson / Rock arch in the 'Castle of Yesnaby' a sandstone sea stack, Yesnaby, Orkney, Scotland, UK, May 2009

Robert Thompson / Hieroglyphics lichen {Graphis scripta} on rock, Castle Coole, Enniskillen, County Fermanagh, Northern Ireland, October

Tim Fitzharris / Granite boulders, Castle Rocks State Park, Idaho

Tim Fitzharris / Granite formations, Castle Rocks State Park, Idaho

Carol Walker / Purebred black Friesian stallion being trained to perform the 'spanish walk', Castle Rock, Colorado, USA Model released

Carol Walker / Purebred black Friesian stallion being trained to perform a 'terre a terre', Castle Rock, Colorado, USA Model released

Carol Walker / Pinto Rocky Mountain stallion running, Castle Rock, Colorado, USA

Carol Walker / Black Friesian gelding running, Castle Rock, Colorado, USA

Carol Walker / Buckskin Morgan mare running, Castle Rock, Colorado, USA

Carol Walker / Purebred bay Rocky Mountain gelding cantering, Castle Rock, Colorado, USA

Carol Walker / Dutch Warmblood gelding with rider, Castle Rock, Colorado, USA Model released

Carol Walker / Purebred chocolate Rocky Mountain stallion trotting / gaiting, Castle Rock, Colorado, USA

Carol Walker / Purebred grey Andalusian stallion learning to do Jambette, Castle Rock, Colorado, USA, Model released

Carol Walker / Purebred grey Rocky Mountain mare cantering, Castle Rock, Colorado, USA

Carol Walker / Purebred grey Andalusian mare wearing horsehair bridle decoration, Moscera, Castle Rock, Colorado, USA,

Carol Walker / Purebred bay Andalusian stallion being trained to perform the 'spanish walk', rider holding a garroche, Castle Rock, Colorado, USA Model released

Carol Walker / Purebred grey Andalusian stallion being trained to perform the Spanish Walk, rider in traditional Spanish attire, Castle Rock, Colorado, USA Model released

Carol Walker / Purebred bay Andalusian stallion being trained to perform the passage, Castle Rock, Colorado, USA Model released

Carol Walker / Purebred bay Andalusian stallion being trained to perform the 'spanish walk', rider holding a garroche, Castle Rock, Colorado, USA Model released

Carol Walker / Purebred grey Andalusian stallion being trained to perform the Levade, rider in traditional Spanish attire, Castle Rock, Colorado, USA Model released

Carol Walker / Purebred black Friesian stallion in Spanish costume, Castle Rock, Colorado, USA Model released

Kirkendall-Spring / The Castle, Capitol Reef National Park, Utah, USA

Kirkendall-Spring / The Castle in Capitol Reef National Park, Utah, USA

Kirkendall-Spring / Spires of rock and mudstone along the Castle Trail in the North Unit of Badlands National Park, South Dakota, USA.

Carol Walker / Bay half Andalusian / half Percheron gelding and bay Quarter Horse gelding running together in field, Castle Rock, Colorado, USA

Carol Walker / Woman with Bay Appendix Quarter horse gelding, Castle Rock, Colorado, USA, model released

Carol Walker / Bay half Andalusian / half Percheron gelding and bay Quarter Horse gelding running together in field, Castle Rock, Colorado, USA

Carol Walker / Sorrel Quarter Horse stallion galloping in paddock, Castle Rock, Colorado, USA

Carol Walker / Woman riding Bay Appendix Quarter horse gelding, Castle Rock, Colorado, USA, model released

Carol Walker / Sorrel Quarter Horse stallion trotting in field, Castle Rock, Colorado, USA

Colin Monteath / Hiker walking near eroded limestone boulders, Castle Hill Basin, Canterbury, New Zealand

Juan Manuel Borrero / Cathar Castle of Quéribus preched on a rocky outcrop, France

Juan Manuel Borrero / Cathar Castle of Quéribus preched on a rocky outcrop, France

Tony Heald / Bearded vulture {Gypaetus barbatus} on rock. Giants castle, South Africa

Kirkendall-Spring / View along Castle Trail, Badlands NP, South Dakota, USA

Colin Monteath / Castle Hill limestone boulders, walker explores boulders in winter, near Christchurch, New Zealand

Tim Edwards / Yesnaby Castle sea stack, Orkney Is, Scotland, UK, at stormy sunset

Tim Fitzharris / Wind and rain eroded rock formations called Molly's Castle, Goblin Valley State Park, Utah

Pat De La Harpe / Portrait of Rock dove (Columba livia), Giants Castle Game Reserve, South Africa

Pat De La Harpe / Verreaux's / Black eagle (Aquila verreauxii) standing on rock, Giants Castle Game Reserve, South Africa

Tony Heald / Male Cape rock thrush {Monticola rupestris} Giants Castle, South Africa

Hanne & Jens Eriksen / Cape Rock Thrush {Monticola rupestris} profile perching on branch, Giant Castle, South Africa.

David Welling / 'The Castle' rock formation, Capitol Reef NP, Utah, USA

Hanne & Jens Eriksen / Giant Castle Game Reserve, Drakensberg, Natal, South Africa

TIM MARTIN / Yesnaby Castle seastack, Pentland Firth, Orkney, Scotland, UK.

Jose B. Ruiz / La Calahorra castle and palace, 16th century. Sierra Nevada, Granada, Spain, Europe

Leo Mandy Dickinson / North Gaulton castle, off Orkney Scotland

Jose B. Ruiz / Spanish castle, Sax, Alicante, Spain, Europe

Tony Heald / Cape rock thrush female {Monticola rupestris} Giants Castle, South Africa

Tony Heald / Cape rock thrush male {Monticola rupestris} Giants Castle, South Africa

Jeff Foott / Fremont Cottonwood (Populus fremontii) trees and rock formation, The Castle, Capitol Reef National Park, Utah

Jeff Foott / Fremont Cottonwood (Populus fremontii) trees and rock formation, The Castle, Capitol Reef National Park, Utah

Jeff Foott / Fremont Cottonwood (Populus fremontii) trees and rock formation, The Castle, Capitol Reef National Park, Utah

Jeff Foott / Rock formation in winter, The Castle, Capitol Reef National Park, Utah

Jeff Foott / Fremont Cottonwood (Populus fremontii) trees and rock formation, The Castle, Capitol Reef National Park, Utah

Jeff Foott / Cottonwood (Populus sp) tree and rock formation in autumn, The Castle, Capitol Reef National Park, Utah

Tim Fitzharris / Shrubland and granite rock formations, Castle Rocks State Park, Idaho