Castell Coch (the Red Castle) in autumn, on the outskirts of Cardiff, Wales, United Kingdom, Europe

Cromwell's Castle, Isle of Tresco, Isles of Scilly, United Kingdom, Europe

Aerial vista of Cadbury Castle Iron Age Hillfort, Devon, England, United Kingdom, Europe

View of Edinburgh Castle, Balmoral Hotel and Princes Street from Calton Hill at dusk, UNESCO World Heritage Site, Edinburgh, Lothian, Scotland, United Kingdom, Europe

View of Edinburgh Castle, Balmoral Hotel and Dugald Stewart monument from Calton Hill at dusk, UNESCO World Heritage Site, Edinburgh, Lothian, Scotland, United Kingdom, Europe

The ruins of Okehampton Castle at sunrise, Okehampton, Devon, England, United Kingdom, Europe

Prague Castle and gardens of Petrin Hill, Prague, Czech Republic (Czechia), Europe

Castel del Monte, UNESCO World Heritage Site, Apulia, Italy, Europe

Medieval Castle of Pandeli, Leros Island, Dodecanese, Greek Islands, Greece, Europe

Medieval Castle and Windmills of Pandeli, Leros Island, Dodecanese, Greek Islands, Greece, Europe

An old window surrounded by ornate carving in the Castle Hill section of Buda, Budapest, Hungary, Europe

Sunrise at Haldon Belvedere (Lawrence Castle) in winter, Devon, England, United Kingdom, Europe

Kilchurn Castle reflected in Loch Awe at dawn in winter, Highlands, Scotland, United Kingdom, Europe

Eilean Donan Castle on Loch Duich in the Scottish Highlands, Scotland, United Kingdom, Europe

Elevated view of Conwy Castle, UNESCO World Heritage Site, and Conwy River visible in background, Conwy, Gwynedd, North Wales, United Kingdom, Europe

Cliffords Tower, York, Yorkshire, England, United Kingdom, Europe

The Royal Castle and Krakow Cathedral, Wawel Hill, Vistula River, Krakow, Poland

Kilchurn Castle and Loch Awe, Highlands Region, Scotland, UK, Europe

Garden Castle Reserve, Drakensberg Mountains, KwaZulu-Natal, South Africa, Africa

Aerial view of the abandoned ruins of Corfe Castle at sunrise, Dorset, England, United Kingdom, Europe

View of Castle, Balmoral Hotel and Princes Street from Calton Hill, Edinburgh, Scotland, United Kingdom, Europe

Medieval Castle of Pandeli, Leros Island, Dodecanese, Greek Islands, Greece, Europe

Windmills of Pandeli, Leros Island, Dodecanese, Greek Islands, Greece, Europe

View from Gellert Hill to Buda Castle, Danube River and Parliament, Budapest, Hungary, Europe

Aerial view by drone of Tsarevets fortress, Veliko Tarnovo, Bulgaria, Europe

Grumello castle illuminated by sun, Sondrio, Valtellina, Lombardy, Italy, Europe

Ross Castle in the evening sunlight, Killarney, County Kerry, Munster, Republic of Ireland, Europe

View of South Bay looking towards Scarborough Castle, Scarborough, Yorkshire, England, United Kingdom, Europe

View over the Cathedral Basilica towards the Castle Hill and Gediminas Tower, Old Town, Vilnius, Lithuania

Panoramic view from Forchtenstein Castle, Burgenland, Austria, Europe

Stone statues, Castle Hill area, Budapest, Hungary, Europe

Buffavento, Byzantine watch tower rebuilt as a castle by Lusignans in the 12th century, highest of Kyrenian hill castles, North Cyprus, Cyprus, Europe

Xativa castle at dusk, at a height of 310 metres above the modern-day city, Xativa, Valencia, Spain, Europe

Mutrah, Muscat, Oman, Middle East

Medieval Castle and Windmills of Pandeli with stormy weather, Leros Island, Dodecanese, Greek Islands, Greece, Europe

Aerial view of Haldon Belvedere Tower (Lawrence Castle) on a sunny late summer morning, Haldon, Devon, England, United Kingdom, Europe

Clifford's Tower, York, Yorkshire, England, United Kingdom, Europe

Corfe Castle at sunrise, Dorset, England, United Kingdom, Europe

Glenveagh castle on lake Lough Beagh in the Glenveagh National Park, County Donegal, Ulster, Republic of Ireland, Europe

Alconchel castle near Badajoz in Spanish Extremadura, Spain, Europe

Bourscheid Castle, Bourscheid, Luxembourg, Europe

Burghausen Castle in Burghausen, Germany, Europe

Schloss Hohenschwangau and the Alpsee lake, Southern Bavaria

Mont Orgueil Castle, Gorey Harbour, Jersey, Channel Islands

Hohenzollern Castle in early morning fog, Hechingen, Swabian Alb, Baden Wurttemberg, Germany, Europe

Concentric star trail over a medieval castle in the Italian countryside, Emilia Romagna, Italy, Europe

Corfe Castle, Corfe, Dorset, England, United Kingdom, Europe

Medieval Castle and Windmills of Pandeli, Leros Island, Dodecanese, Greek Islands, Greece, Europe

Castel del Monte, UNESCO World Heritage Site, Apulia, Italy, Europe

Platanos and Medieval Castle of Pandeli, Agia Marina, Leros Island, Dodecanese, Greek Islands, Greece, Europe

Medieval Castle of Pandeli, Leros Island, Dodecanese, Greek Islands, Greece, Europe

A couple walking up the hill in Castle Combe with an umbrella protecting them from the heavy snowfall, Wiltshire, England, United Kingdom, Europe

Burg Hohenzollern Castle, Zollernalb, Schwaebische Alb (Swabian Alb), Baden Wurttemberg, Germany, Europe

Fisherman's Bastion, Buda Castle Hill, Budapest, Hungary, Europe

View over Lindos town, Rhodes, Dodecanese, Greek Islands, Greece, Europe

Elevated view of Conwy Castle, UNESCO World Heritage Site, and Conwy River visible in background, Conwy, Gwynedd, North Wales, United Kingdom, Europe

Tamworth Castle, Tamworth, Staffordshire, England, United Kingdom, Europe

Chateau de Gruyeres, Gruyeres, Fribourg Canton, Switzerland

Medieval Castle and Windmills of Pandeli, Leros Island, Dodecanese, Greek Islands, Greece, Europe

Esch Sur Sure Castle, Esch Sur Sure, Luxembourg

View from Corfe Castle, Corfe, Dorset, England, United Kingdom, Europe

Platanos and Medieval Castle of Pandeli, elevated view, Agia Marina, Leros Island, Dodecanese, Greek Islands, Greece, Europe

Castello del Buon Consiglio. Trento, Trentino Alto Adige, Italy, Europe

Alconchel Castle near Badajoz in Spanish Extremadura, Spain, Europe

Almourol Castle on the Tagus River, Ribatejo, Portugal, Europe

View of Edinburgh Castle, Balmoral Hotel and Dugald Stewart monument from Calton Hill at dusk, UNESCO World Heritage Site, Edinburgh, Lothian, Scotland, United Kingdom, Europe

Castle of Kaysersberg, Alsace, Alsatian Wine Route, Haut-Rhin, France, Europe

Dumbarton Rock and Castle, Storm Clouds, Firth of Clyde, Scotland, United Kingdom, Europe

View over Cochem with Cochem Castle in the background, Moselle Valley, Rhineland-Palatinate, Germany, Europe

Hohnstein Castle in Saxony, Germany, Europe

Vianden Castle, Vianden Town, Luxembourg

Ruins of Castelo dos Mouros, Sintra, Portugal

Windmills of Pandeli, Leros Island, Dodecanese, Greek Islands, Greece, Europe

Agia Marina Waterfront and Medieval Castle of Pandeli, Leros Island, Dodecanese, Greek Islands, Greece, Europe

Windmills of Pandeli with Medieval Castle in the background, Leros Island, Dodecanese, Greek Islands, Greece, Europe

Matthias Church, Fisherman's Bastion, Buda Castle Hill, Budapest, Hungary, Europe

Alegrete, a dramatic Portuguese medieval hill-top village near Portalegre in the Alentejo region bordering Spain, Portugal, Europe

Bamburgh Castle and its beach, at Bamburgh, near Seahouses, Northumberland, England, United Kingdom, Europe

View of Edinburgh Castle from Princes Street at sunset, UNESCO World Heritage Site, Edinburgh, Scotland, United Kingdom, Europe

View of Edinburgh Castle, Balmoral Hotel and city skyline from Calton Hill at golden hour, Edinburgh, Lothian, Scotland, United Kingdom, Europe

View of Scarborough Castle, Scarborough, Yorkshire, England, United Kingdom, Europe

Castle ruins overlooking the town, Valkenburg, Netherlands, Europe

Castel del Monte on top of a hill surrounded by trees, aerial view, UNESCO World Heritage Site, Apulia, South of Italy, Italy, Europe

Fishermans Bastion, Castle Hill area, Budapest, Hungary, Europe

View from Eichfelsen Rock on Schloss Werenwag Castle and Danube Valley at sunrise, Upper Danube Nature Park, Swabian Alb, Baden Wurttemberg, Germany, Europe

Castle Dogubayazit, Ishak Pasa Sarayi, Turkey - Kurdistan

Morning light, Eglise Notre-Dame-des-Anges, Collioure, Pyrenees-Orientales, Languedoc, France, Europe

Vianden, Luxembourg, Benelux

The Alcazaba old Moorish castle and fortress on hilltop at sunrise, Almeria, Andalusia, Spain

Aerial view of St. Michael's Mount at dawn, Marazion, Cornwall, England, United Kingdom, Europe

Hohenzollern Castle in autumn, Swabian Alps, Baden-Wurttemberg, Germany, Europe

Criccieth Castle, above Criccieth Beach, Gwynedd, North Wales, Wales, United Kingdom, Europe

View of Edinburgh Castle, Balmoral Hotel and Dugald Stewart monument from Calton Hill at dusk, UNESCO World Heritage Site, Edinburgh, Lothian, Scotland, United Kingdom, Europe

Vines on hill on front of Castiglione di Garfagnana, Tuscany, Italy, Europe

Gediminas Tower, Castle Hill, Vilnius, Lithuania

View from Mildenburg Castle over the old town of Miltenberg, Lower Franconia, Bavaria, Germany, Europe

Radicofani, Orcia Valley, Tuscany, Italy, Europe

Tossa de Mar, Costa Brava, Catalunya (Catalonia) (Cataluna), Spain, Europe

Aerial of the Genoese fortress of Sudak, Crimea, Russia, Europe

View over Temo River of Bosa and Malaspina castle, Oristano district, Sardinia, Italy, Mediterranean, Europe