| Olivenza | Olivenza | Spain, Olivenza | -- | -- | | | |
| Odder | Odder | Denmark, Odder | -- | -- | | | |
| Oravice | Oravice | Slovak Republic, Oravice | -- | -- | | | |
| Osimo | Osimo | Italy | -- | -- | | | |
| Opera House | Opera House | United States, Telluride | -- | -- | | | |
| Oituz | Oituz | Romania, Oituz | -- | -- | | | |
| Oppdal | Oppdal | Norway, Oppdal | -- | -- | | | |
| Opole | Opole | Poland, Opole | -- | -- | | | |
| Oranienburg | Oranienburg | Germany, Oranienburg | -- | -- | | | |
| Ornans | Ornans | France, Ornans | -- | -- | | | |
| Obârşia | Obârşia | Romania, Obârşia | -- | -- | | | |
| Oulu | Oulu | Finland, Oulu | -- | -- | | | |
| Opera House | Opera House | United States, Wyoming, Wyoming | -- | -- | | | |
| Ocna Sibiului | Ocna Sibiului | Romania, Ocna Sibiului | -- | -- | | | |
| Ostróg | Ostróg | Poland, Ostróg | -- | -- | | | |
| Ornö | Ornö | Sweden, Ornö | -- | -- | | | |
| Odessa | Одеса (Odessa) | Ukraine, Odessa | -- | -- | | | |
| Ogra | Ogra | Romania, Ogra | -- | -- | | | |
| Ostrava | Ostrava | Czech Republic, Ostrava | -- | -- | | | |
| Oddfellows' Hall | Oddfellows' Hall | Australia, Wagga Wagga, Fitzmaurice Street | -- | -- | | | |
| OSCO - Open Space Hannover | OSCO - Open Space Hannover | Germany, Hannover, Fössestraße 103 | 2019-11-14 | 2019-11-17 | 2019 | 1 | |
| Oakland University | Oakland University | United States, Rochester, 2200 North Squirrel Road | 1972-03-02 | 1972-03-26 | 1972 | 1 | |
| Osservatorio, Teatro | Teatro Osservatorio | Italy, Bari, Trento 12 | 2017-05-07 | -- | 2017 | 1 | |
| Opernhaus | Opernhaus | Germany, Essen | 1942-04-19 | -- | 1942 | 1 | |
| Opera House | Opera House | United States, Bemidji | 1904-09-20 | 1904-09-20 | 1904 | 1 | |
| Opera House | Opera House | United States, Santa Cruz | 1905-07-28 | 1905-07-28 | 1905 | 1 | |
| Oblastnoj teatr dramy | Oblastnoj teatr dramy | Russia, Novosibirsk, Bol'shevistskaya Ulitsa, 45 | 1987-11- | -- | 1987 | 1 | |
| Opernzelt | Opernzelt | Germany, Heidelberg, Emil-Maier-Straße 16 | 2011-04-29 | 2011-07-05 | 2011 | 1 | |
| Odensbacken | Odensbacken | Sweden | 2002-09-12 | -- | 2002 | 1 | |
| Orkanger gymnas | Orkanger gymnas | Norway, Orkanger | 1970-02-13 | -- | 1970 | 1 | |
| Opernhaus, Städtische Theater Karl-Marx-Stadt | Städtische Theater Karl-Marx-Stadt (Opernhaus) | Germany, Karl-Marx-Stadt (Chemnitz), Theaterplatz | 1956-04-29 | -- | 1956 | 1 | |
| Olofström | Olofström | Sweden, Olofström | 1992-11-12 | -- | 1992 | 1 | |
| Omskiy Gosudarstvennyy Dramaticheskiy Pyatyy Teatr | Omskiy Gosudarstvennyy Dramaticheskiy Pyatyy Teatr | Russia, Omsk, ul. Krasnyy Put' 153 | 2005-10-01 | -- | 2005 | 1 | |
| Oslo Domkirke | Oslo Domkirke | Norway, Oslo, Karl Johans gate 11 | 2018-02-09 | 2018-02-10 | 2018 | 1 | |
| Odd Duck Studio | Odd Duck Studio | United States, Seattle, 1214 10th Avenue | 2008-11-26 | 2008-12-20 | 2008 | 1 | |
| ONYX - Théâtre de Saint-Herblain | ONYX - Théâtre de Saint-Herblain | France, Saint-Herblain, 1 Place Océane | 2014-01-31 | -- | 2014 | 1 | |
| Odyssée, L' | L'Odyssée | France, Périgueux, Esplanade Robert Badinter | 2017-01-12 | 2017-01-13 | 2017 | 1 | |
| Oberlin College & Conservatory, Hall auditorium | Oberlin College & Conservatory | United States, Oberlin, 67 North Main St. | 2014-04-17 | 2014-04-19 | 2014 | 1 | |
| Ontmoetingscentrum Aalbeke | Ontmoetingscentrum Aalbeke | Belgium, Aalbeke, Aalbekeplaats | 2001-03-12 | 2001-03-12 | 2001 | 1 | |
| Oslo Rådhus | Oslo Rådhus | Norway, Oslo, Rådhusplassen 1 | 2009-03-28 | -- | 2009 | 1 | |
| Oddemarka skole | Oddemarka skole | Norway, Kristiansand, Kristiansand | 2006-11-08 | -- | 2006 | 1 | |
| Opernhaus Unter den Linden | Opernhaus Unter den Linden | Germany, Berlin | 1905-09-20 | -- | 1905 | 1 | |
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