| Offenburg Stadthalle | Offenburg Stadthalle | Germany, Offenburg, Schutterwälder Str. 3 | 1997-10-22 | 1997-10-22 | 1997 | 1 | |
| Oslo Nye Dukketeater | Oslo Nye Dukketeater | Norway, Oslo | 1994-08-23 | -- | 1994 | 1 | |
| Observatoriet | Observatoriet | Norway, Oslo, Observatoriegata 1 | 2007-06-12 | 2007-08-17 | 2007–2013 | 2 | |
| Orkanger gymnas | Orkanger gymnas | Norway, Orkanger | 1970-02-13 | -- | 1970 | 1 | |
| Opera House | Opera House | United States of America, Telluride | -- | -- | | | |
| Oddemarka skole | Oddemarka skole | Norway, Kristiansand, Kristiansand | 2006-11-08 | -- | 2006 | 1 | |
| Oslo Public Library | Oslo Public Library | Norway, Oslo, Arne Garborgs plass 4 | 1988-06-30 | -- | 1988 | 1 | |
| Oldenburgisches Staatstheater | Oldenburgisches Staatstheater | Germany, Oldenburg, Theaterwall 28 | 1918-11-30 | 2015-12-20 | 1918–2015 | 12 | |
| Opernzelt | Opernzelt | Germany, Heidelberg, Emil-Maier-Straße 16 | 2011-04-29 | 2011-07-05 | 2011 | 1 | |
| Orosháza | Orosháza | Hungary, Orosháza | 1890-05-12 | -- | 1890–1926 | 6 | |
| Odense | Odense | Denmark, Odense | 1948-04-20 | -- | 1948–2000 | 2 | |
| Opernhaus, Städtische Theater Karl-Marx-Stadt | Städtische Theater Karl-Marx-Stadt (Opernhaus) | Germany, Karl-Marx-Stadt (Chemnitz), Theaterplatz | 1956-04-29 | -- | 1956 | 1 | |
| Örkény István Színház | Örkény István Színház | Hungary, Budapest, Madách Imre tér 6 | 2012-03-17 | -- | 2012 | 1 | |
| OSCO - Open Space Hannover | OSCO - Open Space Hannover | Germany, Hannover, Fössestraße 103 | 2019-11-14 | 2019-11-17 | 2019 | 1 | |
| Oslo Domkirke | Oslo Domkirke | Norway, Oslo, Karl Johans gate 11 | 2018-02-09 | 2018-02-10 | 2018 | 1 | |
| Opera House | Opera House | United States of America, Altoona | 1904-03-14 | 1904-03-14 | 1904 | 1 | |
| Orkdal Kulturhus | Orkdal Kulturhus | Norway, Orkanger, Allfarveg 7300 | 2012-11-11 | 2020-10-29 | 2012–2020 | 5 | |
| Ouagadougou, Carrefour Internationale de Théâtre de Ouagadougou | Carrefour Internationale de Théâtre de Ouagadougou | Burkina Faso, Bilbalogho, Ouagadougou, Burkina Faso | 2002-07-13 | -- | 2002 | 1 | |
| Orăștie | Orăștie | Romania, Orăștie | 1911-02-16 | -- | 1911 | 1 | |
| Ohio State University | Ohio State University | United States of America, Columbus, 1739 North High Street | 1981-02-27 | 2001-03-04 | 1981–2001 | 2 | |
| Odyssée, L' | L'Odyssée | France, Périgueux, Esplanade Robert Badinter | 2017-01-12 | 2017-01-13 | 2017 | 1 | |
| Officina Giovani - Cantieri Culturali Ex Macelli | Officina Giovani - Cantieri Culturali Ex Macelli | Italy, Prato, Piazza Macelli, 4 | 2007-04-21 | -- | 2007 | 1 | |
| Oblastnoj teatr dramy | Oblastnoj teatr dramy | Russia, Novosibirsk, Bol'shevistskaya Ulitsa, 45 | 1987-11- | -- | 1987 | 1 | |
| Opera House | Opera House | United States of America, Wyoming, Wyoming | -- | -- | | | |
| Ostseebad Göhren | Ostseebad Göhren | Germany, Göhren | 2010-05-04 | -- | 2010 | 1 | |
| Odenkirchen | Odenkirchen | Germany, Odenkirchen | 1893-10-07 | -- | 1893 | 1 | |
| Odense Teater | Odense Teater | Denmark, Odense, Jernbanegade 21 | 1928-04-30 | 2018-10-13 | 1928–2018 | 16 | |
| Opéra-Théâtre i Avignon | Opéra-Théâtre i Avignon | France, Avignon, 1 Rue Racine | 2012-07-18 | 2012-07-25 | 2012 | 1 | |
| Opera House | Opera House | United States of America, Detroit | 1896-02-18 | 1910-09-28 | 1896–1910 | 2 | |
| Ontmoetingscentrum 't Waaigat | Ontmoetingscentrum 't Waaigat | Belgium, Zwijndrecht, Kerkplein 1 | 2003-05-06 | 2003-05-06 | 2003 | 1 | |
| ONYX - Théâtre de Saint-Herblain | ONYX - Théâtre de Saint-Herblain | France, Saint-Herblain, 1 Place Océane | 2014-01-31 | -- | 2014 | 1 | |
| Opéra-Théâtre de Limoges | Opéra-Théâtre de Limoges | France, Limoges, 48 rue Jean Jaurès | 2017-05-09 | 2017-05-11 | 2017 | 1 | |
| Orpheum Theatre | Orpheum Theatre | United States of America, Salt Lake City | 1908-06-13 | 1908-06-13 | 1908 | 1 | |
| Odéon Théâtre de l'Europe | Odéon Théâtre de l'Europe | France, 75006 Paris, Place de l'Odéon | 2023-05-12 | 2023-06-09 | 2023 | 1 | |
| Otta Samfunnshus | Otta Samfunnshus | Norway, Otta, Klyphaugvegen 8, 2670 Otta | 1973-09-30 | -- | 1973–1987 | 4 | |
| Other Place, The | The Other Place | England, Stratford-upon-Avon, Warwickshire, Waterside | 1981-07-06 | 1982-07-30 | 1981–1996 | 4 | |
| Oerlenbach | Oerlenbach | Germany, Oerlenbach | 2009-12-19 | -- | 2009 | 1 | |
| Orleneff’s Russian Lyceum | Orleneff’s Russian Lyceum | United States of America, New York, East Third Street | 1906-01-03 | -- | 1906 | 1 | |
| Ódry Színpad | Ódry Színpad | Hungary, Budapest, Vas utca 2 | 1967-12-16 | -- | 1967–2017 | 3 | |
| Oituz | Oituz | Romania, Oituz | -- | -- | | | |
| Obfelden | Obfelden | Switzerland | 2002-04-21 | -- | 2002 | 1 | |
| Ovågen | Ovågen | Norway, Øygarden | 2005-09-04 | -- | 2005 | 1 | |
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