| Ottumwa | Ottumwa | United States, Ottumwa | 1903-11-04 | 1903-11-04 | 1903 | 1 | |
| O'Connell Theatre | O'Connell Theatre | United States, Dekalb, Stevens Building, School of Theatre and Dance Northern Illinois University | 2009-02-19 | 2009-03-01 | 2009 | 1 | |
| Orchard Theatre, the | The Orchard Theatre | England, Dartford, Home Gardens | 1996-03-12 | 1996-03-16 | 1996 | 1 | |
| Odense Teater | Odense Teater | Denmark, Odense, Jernbanegade 21 | 1928-04-30 | 2018-10-13 | 1928–2018 | 16 | |
| Opernhaus Unter den Linden | Opernhaus Unter den Linden | Germany, Berlin | 1905-09-20 | -- | 1905 | 1 | |
| Orlovskii dramatičeskii teatr imeni I. Turgeneva | Orlovskii dramatičeskii teatr imeni I. Turgeneva | Russia, Orel, Orel | 1944-05- | -- | 1944–1964 | 2 | |
| Obârşia | Obârşia | Romania, Obârşia | -- | -- | | | |
| Oskar-Herbig-Halle | Oskar-Herbig-Halle | Germany, Mellrichstadt, Bahnhofstr. 17 | 2004-03-03 | -- | 2004–2011 | 2 | |
| Oslo fengsel | Oslo fengsel | Norway, Oslo, Åkebergveien 11 | 2012-11-27 | -- | 2012 | 2 | |
| Ottawa Little Theatre Group | Ottawa Little Theatre Group | Canada, Ottawa | 1945-12-20 | -- | 1945 | 1 | |
| OC De Buiting | OC De Buiting (Cultuur, gemeenschaps of ontmoetingscentrum) | Belgium, Beringen, Tessenderlosesteenweg 18 | 2007-11-29 | 2007-11-30 | 2007 | 1 | |
| Oskarshamn | Oskarshamn | Sweden, Oskarshamn | 1991-05-03 | 1991-05-03 | 1991–1992 | 2 | |
| Odorheiu Secuiesc | Odorheiu Secuiesc | Romania, Odorheiu Secuiesc | 1911-05-09 | -- | 1911 | 1 | |
| OBOS-gården Wesselsgate 15 | OBOS-gården Wesselsgate 15 | Norway, Oslo, Museumsveien 10 | 2006-05-20 | 2008-06-13 | 2006–2008 | 2 | |
| Odder Theater | Odder Theater | Denmark, Odder | 1905-11-25 | -- | 1905–1907 | 4 | |
| Oxfordshire | Oxfordshire | England | 2020-05-08 | -- | 2020 | 1 | |
| Oslo Konserthus | Oslo Konserthus | Norway, Oslo, Munkedamsveien 14 | 2004-05-26 | 2008-04-18 | 2004–2008 | 2 | |
| Opéra Orchestre national Montpellier Occitanie | Opéra Orchestre national Montpellier Occitanie | France, Montpellier, 11 Boulevard Victor Hugo | 2018-01-12 | 2018-01-13 | 2018 | 1 | |
| Opera Națională București | Opera Națională București | Romania, Bucharest, Bulevardul Mihail Kogălniceanu 70-72 | 2007-05-09 | -- | 2007 | 1 | |
| Odeon de Spiegel | Odeon de Spiegel | Netherlands, Zwolle, Blijmarkt 25 | 2000-04-28 | -- | 2000–2008 | 2 | |
| Oulun Kaupunginteatteri | Oulun Kaupunginteatteri | Finland, Oulu, Kaarlenväylä 2 | 1963-- | 1972-04-27 | 1963–1985 | 3 | |
| Opera House | Opera House | New Zealand, Wellington, 111/113 Manners Street | 1890-11-28 | 1890-11-29 | 1890 | 1 | |
| Oslo | Oslo | Norway, Oslo | 1926-09-12 | 2008-10-02 | 1926–2014 | 10 | |
| Opera House | Opera House | United States, Wyoming, Wyoming | -- | -- | | | |
| Ocna Sibiului | Ocna Sibiului | Romania, Ocna Sibiului | -- | -- | | | |
| Opéra de Rouen | Opéra de Rouen | France, Rouen, 7 rue du Docteur Rambert | 2003-11-29 | 2003-11-30 | 2003 | 1 | |
| Olavskapellet, Borgarsyssel Museum | Olavskapellet, Borgarsyssel Museum | Norway, Sarpsborg, Gamlebygaten 8 | 2006-08-01 | 2006-08-02 | 2006 | 1 | |
| Opera House | Opera House | England, Coventry, 4 Hales Street | 1911-09-11 | 1911-09-14 | 1911 | 1 | |
| Opera House | Opera House | United States, New Ulm | 1905-01-15 | 1905-01-15 | 1905 | 1 | |
| Oranienburg | Oranienburg | Germany, Oranienburg | -- | -- | | | |
| Orange Tree Theatre, The | The Orange Tree Theatre | England, London, 1 Clarence St, Richmond | 1991-10-10 | 2012-12-15 | 1991–2012 | 3 | |
| Opera Comique Theatre | Opera Comique Theatre | England, London | 1889-07-17 | 1895-03-30 | 1889–1895 | 6 | |
| Ovalhouse | Ovalhouse | England, London, 52-54 Kennington Oval | 2018-05-17 | 2018-05-19 | 2018 | 1 | |
| Opéra National de Lorraine | Opéra National de Lorraine | France, Nancy, 1 Rue Sainte-Catherine, | 2013-05-23 | -- | 2013 | 1 | |
| Olten | Olten | Switzerland, Olten | 2003-02-17 | -- | 2003 | 1 | |
| Oppdal Kulturhus | Oppdal Kulturhus | Norway, Oppdal, Inge Krokanns veg 2 | 2009-11-12 | 2015-10-08 | 2009–2017 | 5 | |
| Oda Tiyatrosu | Atatürk Kültür Merkezi Oda Tiyatrosu (AKM Oda Tiyatrosu) | Turkey, Istanbul, Gümüşsuyu Mahallesi, Tak-ı Zafer Cd., Beyoğlu | 1975-- | 1976-- | 1975 | 1 | |
| Opera House | Opera House | United States, Dixon | 1904-11-30 | 1907-12-21 | 1904–1907 | 2 | |
| Osnabrücker Stadttheater | Osnabrücker Stadttheater | Germany, Osnabrück, Große Gildewart 7 | 1894-03-29 | 1900-04-26 | 1894–1909 | 7 | |
| Odda kino | Odda kino | Norway, Odda, Opheimsgata 31, 5750 ODDA | 1969-09-26 | -- | 1969–1978 | 4 | |
| Opera House | Opera House | United States, San Juan | 1905-05-06 | 1905-05-06 | 1905 | 1 | |
| Ohgawara | Ohgawara | Japan, Ohgawara | 2010-02-02 | -- | 2010 | 1 | |
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