| Osimo | Osimo | Italy | -- | -- | | | |
| Ocna Sibiului | Ocna Sibiului | Romania, Ocna Sibiului | -- | -- | | | |
| Odessa | Одеса (Odessa) | Ukraine, Odessa | -- | -- | | | |
| Oravice | Oravice | Slovak Republic, Oravice | -- | -- | | | |
| Oulu | Oulu | Finland, Oulu | -- | -- | | | |
| Ostrava | Ostrava | Czech Republic, Ostrava | -- | -- | | | |
| Olivenza | Olivenza | Spain, Olivenza | -- | -- | | | |
| Opole | Opole | Poland, Opole | -- | -- | | | |
| Opera House | Opera House | United States, Telluride | -- | -- | | | |
| Ogra | Ogra | Romania, Ogra | -- | -- | | | |
| Oranienburg | Oranienburg | Germany, Oranienburg | -- | -- | | | |
| Oppdal | Oppdal | Norway, Oppdal | -- | -- | | | |
| Ornö | Ornö | Sweden, Ornö | -- | -- | | | |
| Oddfellows' Hall | Oddfellows' Hall | Australia, Wagga Wagga, Fitzmaurice Street | -- | -- | | | |
| Odder | Odder | Denmark, Odder | -- | -- | | | |
| Oituz | Oituz | Romania, Oituz | -- | -- | | | |
| Ostróg | Ostróg | Poland, Ostróg | -- | -- | | | |
| Obârşia | Obârşia | Romania, Obârşia | -- | -- | | | |
| Ornans | Ornans | France, Ornans | 2001-- | -- | 2001 | 1 | |
| Opera House | Opera House | United States | 1899-12-20 | 1899-12-20 | 1899 | 1 | |
| Ostersund | Ostersund | Sweden, Ostersund | 1936-10-30 | -- | 1936 | 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 | |
| Ouagadougou, Carrefour Internationale de Théâtre de Ouagadougou | Carrefour Internationale de Théâtre de Ouagadougou | Burkina Faso, Bilbalogho, Ouagadougou, Burkina Faso | 2002-07-13 | -- | 2002 | 1 | |
| Opernhaus Unter den Linden | Opernhaus Unter den Linden | Germany, Berlin | 1905-09-20 | -- | 1905 | 1 | |
| Osobnyak Theatre | Osobnyak Theatre | Russia, St. Petersburg, Kamennoostrovsky 55 | 2011-05-15 | 2011-05-17 | 2011 | 1 | |
| Ottawa Little Theatre Group | Ottawa Little Theatre Group | Canada, Ottawa | 1945-12-20 | -- | 1945 | 1 | |
| Oscarshall | Oscarshall | Norway, Oslo, Oscarshallveien | 2017-08-28 | 2017-11-28 | 2017 | 1 | |
| Opera House | Opera House | United States, Altoona | 1904-03-14 | 1904-03-14 | 1904 | 1 | |
| OPERATTEN im STATTtheater | OPERATTEN im STATTtheater | Switzerland, Stäfa, Bahnhofstrasse 52 | 2007-03-07 | 2007-04-21 | 2007 | 1 | |
| Open Space Theatre | Open Space Theatre | United States, New York | 1982-01-11 | -- | 1982 | 1 | |
| Olofström | Olofström | Sweden, Olofström | 1992-11-12 | -- | 1992 | 1 | |
| Opera Națională București | Opera Națională București | Romania, Bucharest, Bulevardul Mihail Kogălniceanu 70-72 | 2007-05-09 | -- | 2007 | 1 | |
| Overholser Theatre | Overholser Theatre | United States, Ardmore | 1910-12-21 | 1910-12-21 | 1910 | 1 | |
| OC De Buiting | OC De Buiting (Cultuur, gemeenschaps of ontmoetingscentrum) | Belgium, Beringen, Tessenderlosesteenweg 18 | 2007-11-29 | 2007-11-30 | 2007 | 1 | |
| Orleneff’s Russian Lyceum | Orleneff’s Russian Lyceum | United States, New York, East Third Street | 1906-01-03 | -- | 1906 | 1 | |
| Oakland University | Oakland University | United States, Rochester, 2200 North Squirrel Road | 1972-03-02 | 1972-03-26 | 1972 | 1 | |
| Opera House | Opera House | United States, Pensacola | 1903-10-25 | 1903-10-25 | 1903 | 1 | |
| Orkdal Samfunnshus | Orkdal Samfunnshus | Norway, Fannrem | 1978-11-22 | -- | 1978 | 1 | |
| Opera House | Opera House | United States, New Castle | 1907-03-09 | 1907-03-09 | 1907 | 1 | |
| Ontmoetingscentrum d'Iefte | Ontmoetingscentrum d'Iefte | Belgium, Deerlijk, Hoogstraat 122 | 2002-01-14 | 2002-01-15 | 2002 | 1 | |
| Oslo Nye Dukketeater | Oslo Nye Dukketeater | Norway, Oslo, Rosenkrantz' gate 10 | 1994-08-23 | -- | 1994 | 1 | |
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Venues
