| Opera House | Opera House | United States of America, San Bernardino | 1903-12-31 | 1908-12-04 | 1903–1908 | 2 | |
| Origosenteret | Origosenteret | Norway, Svinndal, Tyritoppen 19 | 2012-11-26 | -- | 2012 | 2 | |
| Old Tote Theatre, The | The Old Tote Theatre | Australia, Kensington, High Street | 1967-09-23 | 1971-08-03 | 1967–1971 | 2 | |
| Onde, L' | L'Onde | France, Vélizy-Villacoublay, 8 bis Avenue Louis Breguet | 2015-05-19 | 2018-01-19 | 2015–2018 | 2 | |
| Observatoriet | Observatoriet | Norway, Oslo, Observatoriegata 1 | 2007-06-12 | 2007-08-17 | 2007–2013 | 2 | |
| Oskar-Herbig-Halle | Oskar-Herbig-Halle | Germany, Mellrichstadt, Bahnhofstr. 17 | 2004-03-03 | -- | 2004–2011 | 2 | |
| Országos Kamaraszínház | Országos Kamaraszínház | Hungary, Mezőtúr | 1925-09-23 | -- | 1925–1927 | 2 | |
| Odeon de Spiegel | Odeon de Spiegel | Netherlands, Zwolle, Blijmarkt 25 | 2000-04-28 | -- | 2000–2008 | 2 | |
| Old Town Hall Arts Center | Old Town Hall Arts Center | England, Hertfordshire, Hemel Hempstead | 1985-02-18 | 1985-02-20 | 1985–2011 | 2 | |
| Old American Can Factory, The | The Old American Can Factory | United States of America, Brooklyn, 232 3rd Street | 2003-03-06 | 2003-06-07 | 2003 | 2 | |
| Opera House | Opera House | United States of America, Dixon | 1904-11-30 | 1907-12-21 | 1904–1907 | 2 | |
| Odsherred Teater | Odsherred Teater | Denmark, Nykobing Sjaelland, Annebergparken 22 | 2002-02-27 | -- | 2002–2006 | 2 | |
| Odyssey Theatre | Odyssey Theatre | United States of America, Los Angeles, 2055 S Sepulveda Blvd | 2008-05-02 | 2022-10-23 | 2008–2022 | 2 | |
| Oliver Theatre | Oliver Theatre | United States of America, Lincoln | 1903-05-09 | 1908-11-03 | 1903–1908 | 2 | |
| Old Fire Station Studio Theatre | Old Fire Station Studio Theatre | England, Oxford, 40 George St | 2003-11-11 | 2018-10-06 | 2003–2018 | 2 | |
| Opernhaus | Opernhaus | Germany, Wuppertal, Kurt-Drees-Straße 4 | 2011-06-26 | 2011-12-01 | 2011 | 2 | |
| Opera House | Opera House | United States of America, New Castle | 1904-04-29 | 1908-04-11 | 1904–1908 | 2 | |
| Opera House | Opera House | United States of America, Kentucky, Kentucky | 1899-12-20 | 1903-12-10 | 1899–1903 | 2 | |
| Opernhaus | Opernhaus | Germany, Frankfurt, Opernplatz 1 | 1892-12-10 | -- | 1892–1940 | 2 | |
| Opern- und Schauspielhaus Hannover | Opern- und Schauspielhaus Hannover | Germany, Hannover | 1920-06-21 | -- | 1920–1924 | 2 | |
| Octagon, The | The Octagon | United States of America, Montgomery, 1 Festival Drive | 1997-03-04 | 2002-04-14 | 1997–2002 | 2 | |
| Oriental Vevey | Oriental Vevey | Switzerland, Vevey, Rue d'Italie, 22 | 2018-10-31 | 2018-11-18 | 2018 | 2 | |
| Orfeó Gracienc | Orfeó Gracienc | Spain, Barcelona, Carrer d'Astúries, 83 (Gràcia) | 1910-07- | -- | 1910–1915 | 2 | |
| Ocna Mureș | Ocna Mureș | Romania, Ocna Mureș | 1890-02-06 | -- | 1890–1911 | 2 | |
| Oslo Nye Trikkestallen | Oslo Nye Trikkestallen | Norway, Oslo, Torshovgata 33 | 2011-07-01 | 2019-01-06 | 2011–2019 | 2 | |
| Opera House | Opera House | United States of America, Detroit | 1896-02-18 | 1910-09-28 | 1896–1910 | 2 | |
| Orlovskij dramatičeskij teatr imeni I. Turgeneva | Orlovskij dramatičeskij teatr imeni I. Turgeneva | Russia, Orel, Orel | 1944-05- | -- | 1944–1964 | 2 | |
| Östgötateatern | Östgötateatern | Sweden, Norrköping, Slottsgatan 135 | 1997-11-15 | 2022-03-19 | 1997–2022 | 2 | |
| OBOS-gården Wesselsgate 15 | OBOS-gården Wesselsgate 15 | Norway, Oslo, Museumsveien 10 | 2006-05-20 | 2008-06-13 | 2006–2008 | 2 | |
| Oslo Konserthus | Oslo Konserthus | Norway, Oslo, Munkedamsveien 14 | 2004-05-26 | 2008-04-18 | 2004–2008 | 2 | |
| Ohnsorg Theater | Ohnsorg Theater | Germany, Hamburg, Heidi-Kabel-Platz 1 | 1995-04-24 | 2002-05-25 | 1995–2002 | 2 | |
| Oslo fengsel | Oslo fengsel | Norway, Oslo, Åkebergveien 11 | 2012-11-27 | -- | 2012 | 2 | |
| Oskarshamn | Oskarshamn | Sweden, Oskarshamn | 1991-05-03 | 1991-05-03 | 1991–1992 | 2 | |
| Orikkusu Gekijō | Orikkusu Gekijō (Orix Theater) | Japan, Osaka, 1-14-15 Shin-machi, Nishi-ku | 1971-10-03 | -- | 1971 | 2 | |
| Opernhaus Hannover | Opernhaus Hannover | Germany, Hannover, Opernplatz 1 | 1928-03-06 | 1956-12-05 | 1928–1956 | 2 | |
| Oblasni dram teatr | Oblasni dram teatr | Russia, Kaliningrad, Prospekt Mira, 4 | 1960-01- | -- | 1960–1973 | 2 | |
| Örebro | Örebro | Sweden, Örebro | 1936-09-27 | -- | 1936–1970 | 3 | |
| Ódry Színpad | Ódry Színpad | Hungary, Budapest, Vas utca 2 | 1967-12-16 | -- | 1967–2017 | 3 | |
| Ohkuma Auditorium | Ohkuma Auditorium | Japan, Tokyo, Japan | 1954-09-11 | -- | 1954–1965 | 3 | |
| Orange Tree Theatre, The | The Orange Tree Theatre | England, London, 1 Clarence St, Richmond | 1991-10-10 | 2012-12-15 | 1991–2012 | 3 | |
| Orpheum | Orpheum | Germany, Munich | 1893-03-08 | -- | 1893–1895 | 3 | |
| Oravița | Oravița | Romania, Oravița | 1884-12-08 | 1884-12-23 | 1884–1913 | 3 | |
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