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Ocna Dejului
Ocna Dejului (Désakna), quarter of Dej, Cluj County, Romania; former salt-mining village documented from 1239, Roman-era salina guarded from Gherla, now a balneological resort of flooded salt-mine lakes with 260 g/l brine.
Ocoyoacac
Ocoyoacac (Tlalcozpan) is an INAH archaeological zone in the State of Mexico at km 45.5 of the Mexico-Toluca highway: a Classic-period, possibly Teotihuacan-immigrant settlement with simple rooms and talud-tablero architecture, free to visit Tuesday to Sunday.
OCT Adventure Bay
OCT Adventure Bay (华侨城奇梦海滩水世界, Xiangyang Qimeng Beach Water Park) is an OCT Group water park in Xiangyang, Hubei, China, opened June 24, 2020; 150,000 m², 800 million yuan, four ocean-exploration themed areas, world's first Orbiter slide.
OCT East Knight Valley
Knight Valley (大侠谷) is the amusement park of the OCT East resort in Dameisha, Shenzhen, China, combining mountain canyon scenery with thrill rides like the Wood Coaster.
OCT East Tea Stream Valley
Tea Stream Valley (茶溪谷), leisure and tea-culture district of OCT East resort in Dameisha, Yantian District, Shenzhen; opened 2007 with Interlaken Town, Sanzhou Tea Plantation, Wetland Garden; served by a 12 RMB weekend bus line.
OCT Fantasy Valley
OCT Fantasy Valley (襄阳华侨城奇幻谷) is a space-exploration-themed theme park in Xiangyang, Hubei, opened April 2022 by OCT Group; 4 billion yuan, 450,000 m², six themed zones, B&M wing coaster DaVinci Ride.
Octaviolca
Octaviolca (Ottaviolca), Roman settlement in the Regio Cantabrorum named by Ptolemy and listed on the Itinerario de Barro between Legio VII Gemina and Portus Blendium; usually identified with Rebolledo-Camesa, Valdeolea, Cantabria.
Odawara Castle (小田原城)
Odawara Castle (小田原城), a Japanese castle in Odawara, Kanagawa; mid-15th-century Ōmori origin, Hōjō clan seat from about 1500, 9 km sōgome, Hideyoshi's 1590 siege, 1960 concrete keep.
Odeion of Agrippa
Odeion of Agrippa (Agrippeion), a roofed 1,000-seat concert hall given to Athens by Marcus Vipsanius Agrippa around 15 BC in the center of the Ancient Agora; its 25 m unsupported roof collapsed, and it was rebuilt about AD 150 as a 500-seat philosophy lecture hall.
Odeion of Perikles
Odeion of Perikles (Ωδείον του Περικλέους), a large roofed square hall on Athens' Acropolis south slope, built 447–443/2 BC for Panathenaic musical contests, imitating Xerxes' tent, later rebuilt by Ariobarzanes II.
Odeon at Aphrodisias
Odeon at Aphrodisias: Roman-era roofed concert hall and Bouleuterion (council house) between the Temple of Aphrodite and North Agora; about 1,700 seats, marble stage façade, rebuilt 2nd century AD by the family of Tiberius Claudius Attalos.
Odéon at Carthage
The Odéon at Carthage was a Roman auditorium for music and spoken performance, built under the Severans and second in size only to Rome's Odeon of Domitian.
Odeon at Catania
The Odeon at Catania is a small Roman odeum built in the 2nd century AD west of the ancient theatre on Montevergine hill, Sicily; about 42 m wide, seating roughly 1,500, used for musical and poetic contests, later buried, spoliated, and excavated from the 18th century onward.
Odeon at Hadrian's Villa
The so-called Odeon (South Theatre) at Hadrian's Villa, Tivoli: a private theatre of about 1,100 seats, 55 m cavea, built 133-138 CE; recent scholarship rejects the odeon identification.
Odeon at Kom el-Dikka
Odeon at Kom el-Dikka, Alexandria: Egypt's only Roman theatre-odeon, 13 marble tiers seating 600-800, remodeled in the 6th century into a domed lecture auditorium of the late-antique academic complex.
Odeon in Ptolemais
Odeon in Ptolemais: small Roman odeum at Ptolemais, Cyrenaica, Libya; 32 m cavea, second or third century AD, converted in the fourth or fifth century for water spectacles, later a Byzantine cistern.
Odeon of Herodes Atticus
Odeon of Herodes Atticus (Herodeion), Roman odeon on the Acropolis' southwest slope, built 160-174 CE by Herodes Atticus for his wife Regilla; roofed originally, restored 1952-53, main Athens Epidaurus Festival venue, closed 2026 for restoration.
Odeon of Lyon
Odeon of Lyon: Roman odeon (roofed concert hall) on Fourvière hill at Lugdunum, built late 1st-2nd century AD, 73 m diameter, ~3,000 seats, rare in Gaul, restored 1933-1970.
Odeon of Philippopolis
The Odeon of Philippopolis is an ancient Roman odeon, a small covered theater, uncovered at the Ancient Forum of Plovdiv, Bulgaria, that also housed the city council.
Ödes Schloss bridgehead fort
Ödes Schloss (Öde Schloss, Veste Stopfenreuth), a Roman bridgehead fort near Stopfenreuth, Lower Austria, identified in 2024-2025 excavations; first of its type found in Austria, guarding the Amber Road Danube crossing near Carnuntum.
Odesa Lunapark
Odesa Lunapark (Одеський лунапарк) is an amusement park opened in 2011 in Shevchenko Park, Odesa, Ukraine, near Lanzheron beach. Over 20 rides, a 45 m Ferris wheel, ice rink, Park-Card payments, generator power during blackouts.
Odry
Odry (Odry, Czersk municipality, Poland): a Wielbark culture, Gothic cemetery with 10 stone circles 15-33 m across, 30 barrows, and about 627 flat graves, used from the 70s-80s AD to the early 3rd century AD; protected since 1958 as a 16.91 ha archaeological and nature reserve.
Odsherred UNESCO Global Geopark
Odsherred UNESCO Global Geopark, Denmark's first geopark (EGN/GGN 2014, UNESCO 2015), covers 355 km² of Odsherred Municipality, defined by the Ice Age Odsherred Arches formed 17,000–19,000 years ago.
Oeste UNESCO Global Geopark
Oeste UNESCO Global Geopark, designated by UNESCO in 2024, covers six municipalities on Portugal's central west coast north of Lisbon and is known for dinosaur fossils.
Oga Aquarium GAO
Oga Aquarium GAO (男鹿水族館GAO) is the only aquarium in Akita Prefecture, Japan, in Oga city on the Oga Peninsula. Opened 2004; 815-ton main tank, 400 species, polar bear Gota, hatahata fish, geosite beach.
Oguz
Oguz (Курган Огуз) is a large Scythian royal kurgan in the Black Sea steppe of southern Ukraine, the largest of the region, built in the 4th century BC.
Ohrid-Prespa Biosphere Reserve
Ohrid-Prespa Biosphere Reserve, a UNESCO transboundary biosphere reserve designated in 2014 across Albania and North Macedonia, covering the Ohrid and Prespa lakes, their endemic-rich waters, karst hydrology, and shared conservation challenges.
Oita Marine Palace Aquarium "Umitamago"
Oita Marine Palace Aquarium "Umitamago" (大分マリーンパレス水族館「うみたまご」) is a public aquarium in Oita City, Japan, opened April 1, 2004 on Beppu Bay, known for its 1,250-ton Bungo Channel tank, walrus and dolphin shows, and the Asobeach interactive area.
Okapi Wildlife Reserve
Okapi Wildlife Reserve (Réserve de faune à okapis): ~13,726 km² protected area in the Ituri forest, DRC, created 1992, UNESCO World Heritage Site 1996, in Danger since 1997; holds about 5,000 of 30,000 wild okapi, 17 primate species, and Mbuti and Efe communities; threatened by poaching and gold mining.
Okcheon Nongshim Themed Park
Okcheon Nongshim Themed Park (농심테마공원), a free 32,000 m² agricultural experience park in the Okcheon Agricultural Technology Center, North Chungcheong, linked by walkway to the Gyeongbu Expressway rest area.