| Ontmoetingscentrum d'Iefte | Ontmoetingscentrum d'Iefte | Belgium, Deerlijk, Hoogstraat 122 | 2002-01-14 | 2002-01-15 | 2002 | 1 | |
| Orchard Theatre, the | The Orchard Theatre | England, Dartford, Home Gardens | 1996-03-12 | 1996-03-16 | 1996 | 1 | |
| Osnabrücker Hof | Osnabrücker Hof | Germany, Osnabrück, Kollegienwall 14 | 1896-05-13 | -- | 1896 | 1 | |
| Odorheiu Secuiesc | Odorheiu Secuiesc | Romania, Odorheiu Secuiesc | 1911-05-09 | -- | 1911 | 1 | |
| Orleneff’s Russian Lyceum | Orleneff’s Russian Lyceum | United States, New York, East Third Street | 1906-01-03 | -- | 1906 | 1 | |
| Ovågen | Ovågen | Norway, Øygarden | 2005-09-04 | -- | 2005 | 1 | |
| Överkalix Folkets Hus | Överkalix Folkets Hus | Sweden, Överkalix, Bulandsgatan 2 | 2010-11-16 | -- | 2010 | 1 | |
| Óbudai Kisfaludy Színház | Óbudai Kisfaludy Színház | Hungary, Budapest | 1900-04-15 | -- | 1900 | 1 | |
| Oslo dagene, Akershus Festning | Oslo dagene, Akershus Festning | Norway, Oslo | 1983-08-29 | 1983-09-03 | 1983 | 1 | |
| Opera House | Opera House | United States, Logan | 1905-04-15 | 1905-04-15 | 1905 | 1 | |
| O'Reilly Theatre | O'Reilly Theatre | Ireland, Dublin, Great Denmark Street | 2011-09-27 | 2011-10-16 | 2011 | 1 | |
| Optima Playhouse | Optima Playhouse | Australia, Adelaide, Festival Drive | 1999-07-06 | 1999-07-24 | 1999 | 1 | |
| Orpheum | Orpheum | United States, El Paso | 1908-06-18 | 1908-06-18 | 1908 | 1 | |
| Olomouc | Olomouc | Czech Republic, Olomouc | 2007-05-17 | -- | 2007 | 1 | |
| Ottumwa | Ottumwa | United States, Ottumwa | 1903-11-04 | 1903-11-04 | 1903 | 1 | |
| Overture Center for the Arts, The Playhouse | Overture Center for the Arts, The Playhouse | United States, Madison, 201 State St | 2010-03-18 | 2010-03-28 | 2010 | 1 | |
| Old globe theatre, the | The Old Globe Theatre | United States, San Diego, 1363 Old Globe Way | 1995-04-30 | 1995-06-18 | 1995 | 1 | |
| Oxfordshire | Oxfordshire | England | 2020-05-08 | -- | 2020 | 1 | |
| Ottawa Little Theatre Group | Ottawa Little Theatre Group | Canada, Ottawa | 1945-12-20 | -- | 1945 | 1 | |
| Opera Națională București | Opera Națională București | Romania, Bucharest, Bulevardul Mihail Kogălniceanu 70-72 | 2007-05-09 | -- | 2007 | 1 | |
| Opera House | Opera House | United States, Bemidji | 1904-09-20 | 1904-09-20 | 1904 | 1 | |
| Opéra Orchestre national Montpellier Occitanie | Opéra Orchestre national Montpellier Occitanie | France, Montpellier, 11 Boulevard Victor Hugo | 2018-01-12 | 2018-01-13 | 2018 | 1 | |
| Old Auditorium, Worcester State College | Old Auditorium, Worcester State College | United States, Worcester, 486 Chandler Street | 1971-04-29 | 1971-05-01 | 1971 | 1 | |
| Odensbacken | Odensbacken | Sweden | 2002-09-12 | -- | 2002 | 1 | |
| Opera House | Opera House | England, Coventry, 4 Hales Street | 1911-09-11 | 1911-09-14 | 1911 | 1 | |
| Opera House | Opera House | United States, Santa Cruz | 1905-07-28 | 1905-07-28 | 1905 | 1 | |
| On Pitch Performing Arts CenterOn Pitch Performing Arts Center | On Pitch Performing Arts Center | United States | 2023-09-15 | 2023-09-20 | 2023 | 1 | |
| Old Town Players | Old Town Players | United States, Chicago | 1973-02-09 | 1973-04-15 | 1973 | 1 | |
| Ordway Center for the Performing Arts (Main Hall) | Ordway Center for the Performing Arts (Main Hall) | United States, Saint Paul, 345 Washington St | 2005-10-18 | 2005-10-19 | 2005 | 1 | |
| Opéra National de Lorraine | Opéra National de Lorraine | France, Nancy, 1 Rue Sainte-Catherine, | 2013-05-23 | -- | 2013 | 1 | |
| Omskiy Gosudarstvennyy Dramaticheskiy Pyatyy Teatr | Omskiy Gosudarstvennyy Dramaticheskiy Pyatyy Teatr | Russia, Omsk, ul. Krasnyy Put' 153 | 2005-10-01 | -- | 2005 | 1 | |
| Oslo Public Library | Oslo Public Library | Norway, Oslo, Arne Garborgs plass 4 | 1988-06-30 | -- | 1988 | 1 | |
| Oda Tiyatrosu | Atatürk Kültür Merkezi Oda Tiyatrosu (AKM Oda Tiyatrosu) | Turkey, Istanbul, Gümüşsuyu Mahallesi, Tak-ı Zafer Cd., Beyoğlu | 1975-- | 1976-- | 1975 | 1 | |
| Odd Duck Studio | Odd Duck Studio | United States, Seattle, 1214 10th Avenue | 2008-11-26 | 2008-12-20 | 2008 | 1 | |
| Ovalhouse | Ovalhouse | England, London, 52-54 Kennington Oval | 2018-05-17 | 2018-05-19 | 2018 | 1 | |
| Opera House | Opera House | United States, San Juan | 1905-05-06 | 1905-05-06 | 1905 | 1 | |
| Otto-Klenert-Schule | Otto-Klenert-Schule | Germany, Bad Friedrichshall, Rathausplatz 7 | 2006-02-18 | -- | 2006 | 1 | |
| Ostersund | Ostersund | Sweden, Ostersund | 1936-10-30 | -- | 1936 | 1 | |
| Ontmoetingscentrum Aalbeke | Ontmoetingscentrum Aalbeke | Belgium, Aalbeke, Aalbekeplaats | 2001-03-12 | 2001-03-12 | 2001 | 1 | |
| Oscarshall | Oscarshall | Norway, Oslo, Oscarshallveien | 2017-08-28 | 2017-11-28 | 2017 | 1 | |
| Oberschlesisches Grenzlandtheater Ratibor | Oberschlesisches Grenzlandtheater Ratibor | Poland, Ratibor / Racibórz | 1937-02-19 | -- | 1937 | 1 | |
| Orăștie | Orăștie | Romania, Orăștie | 1911-02-16 | -- | 1911 | 1 | |
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