| Orkanger gymnas | Orkanger gymnas | Norway, Orkanger | 1970-02-13 | -- | 1970 | 1 | |
| Old Courthouse | Old Courthouse | Northern Ireland, Antrim, Market Square | 2011-05-26 | -- | 2011 | 1 | |
| Olathe Opera House | Olathe Opera House | United States, Olathe | 1908-01-31 | 1908-01-31 | 1908 | 1 | |
| Oravice | Oravice | Slovak Republic, Oravice | -- | -- | | | |
| Olofström | Olofström | Sweden, Olofström | 1992-11-12 | -- | 1992 | 1 | |
| Oslo Nye Dukketeater | Oslo Nye Dukketeater | Norway, Oslo, Rosenkrantz' gate 10 | 1994-08-23 | -- | 1994 | 1 | |
| Oblastnoi dramatičeskij teatr | Oblastnoi dramatičeskij teatr | Russia, Veliky Novgorod | 1948-09- | -- | 1948 | 1 | |
| Oldenburgisches Staatstheater | Oldenburgisches Staatstheater | Germany, Oldenburg, Theaterwall 28 | 1918-11-30 | 2015-12-20 | 1918–2015 | 12 | |
| Ophelia Theater | Ophelia Theater | United States, Astoria, 21-12 30th Road | 2016-10-28 | 2016-11-13 | 2016 | 1 | |
| O'Reilly Theatre | O'Reilly Theatre | Ireland, Dublin, Great Denmark Street | 2011-09-27 | 2011-10-16 | 2011 | 1 | |
| Opéra de Rouen | Opéra de Rouen | France, Rouen, 7 rue du Docteur Rambert | 2003-11-29 | 2003-11-30 | 2003 | 1 | |
| Odense Theater | Odense Theater | Denmark, Odense, Sortebrødre Torv | 1876-04-20 | 1899-10-20 | 1876–1901 | 9 | |
| Ovågen | Ovågen | Norway, Øygarden | 2005-09-04 | -- | 2005 | 1 | |
| Oblastnoj teatr dramy | Oblastnoj teatr dramy | Russia, Čeljabinsk | 1980-09- | -- | 1980 | 1 | |
| Ódry Színpad | Ódry Színpad | Hungary, Budapest, Vas utca 2 | 1967-12-16 | -- | 1967–2017 | 3 | |
| Otta | Otta | Norway, Otta | 1971-03-19 | -- | 1971–2004 | 4 | |
| Opernhaus Graz | Opernhaus Graz | Austria, Graz, Opernring | 1912-05-24 | -- | 1912 | 2 | |
| Opéra National de Lorraine | Opéra National de Lorraine | France, Nancy, 1 Rue Sainte-Catherine, | 2013-05-23 | -- | 2013 | 1 | |
| Óbudai Kisfaludy Színház | Óbudai Kisfaludy Színház | Hungary, Budapest | 1900-04-15 | -- | 1900 | 1 | |
| Oulun Kaupunginteatteri | Oulun Kaupunginteatteri | Finland, Oulu, Kaarlenväylä 2 | 1963-- | 1972-04-27 | 1963–1985 | 3 | |
| Oscarsborg Festning | Oscarsborg Festning | Norway, Oscarsborg, Husvikveien | 2006-07-27 | 2007-06-24 | 2006–2007 | 2 | |
| Oxfordshire | Oxfordshire | England | 2020-05-08 | -- | 2020 | 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 | |
| Odda | Odda | Norway, Odda | 1951-04-25 | 1958-03-02 | 1951–1982 | 6 | |
| Ottumwa | Ottumwa | United States, Ottumwa | 1903-11-04 | 1903-11-04 | 1903 | 1 | |
| Ogra | Ogra | Romania, Ogra | -- | -- | | | |
| Opera House | Opera House | United States, New Ulm | 1905-01-15 | 1905-01-15 | 1905 | 1 | |
| Odensbacken | Odensbacken | Sweden | 2002-09-12 | -- | 2002 | 1 | |
| Oulu | Oulu | Finland, Oulu | -- | -- | | | |
| Owl Spot | Owl Spot | Japan, Tokyo | 2009-02-04 | 2016-11-23 | 2009–2016 | 7 | |
| Opernhaus | Opernhaus | Germany, Wuppertal, Kurt-Drees-Straße 4 | 2011-06-26 | 2011-12-01 | 2011 | 2 | |
| Oosterpoort Groningen, De | De Oosterpoort Groningen | Netherlands, 9724 DA, Trompsingel 27, | 2000-04-20 | 2000-04-21 | 2000 | 1 | |
| Opera House | Opera House | United States, Logan | 1905-04-15 | 1905-04-15 | 1905 | 1 | |
| Örkény István Színház | Örkény István Színház | Hungary, Budapest, Madách Imre tér 6 | 2012-03-17 | -- | 2012 | 1 | |
| Optima Playhouse | Optima Playhouse | Australia, Adelaide, Festival Drive | 1999-07-06 | 1999-07-24 | 1999 | 1 | |
| Oseana Kunst & Kultursenter | Oseana Kunst & Kultursenter | Norway, Os, Mobergsbakken 20 | 2012-09-18 | 2020-09-13 | 2012–2020 | 5 | |
| Oslo Nye Trikkestallen | Oslo Nye Trikkestallen | Norway, Oslo, Torshovgata 33 | 2011-07-01 | 2019-01-06 | 2011–2019 | 2 | |
| Ogólnopolski Festiwal Sztuki Reżyserskiej INTERPRETACJE | Ogólnopolski Festiwal Sztuki Reżyserskiej INTERPRETACJE | Poland, Katowice, Sejmu Śląskiego 2 | 2016-11-12 | 2016-11-12 | 2016 | 1 | |
| Opera House | Opera House | United States, Santa Cruz | 1905-07-28 | 1905-07-28 | 1905 | 1 | |
| Odda ungdomsskole | Odda ungdomsskole | Norway, Odda, Eidesmoen | 2006-11-15 | -- | 2006 | 1 | |
| Ostrava | Ostrava | Czech Republic, Ostrava | -- | -- | | | |
| Olivenza | Olivenza | Spain, Olivenza | -- | -- | | | |
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