| Opera House | Opera House | United States of America, San Juan | 1905-05-06 | 1905-05-06 | 1905 | 1 | |
| ONYX - Théâtre de Saint-Herblain | ONYX - Théâtre de Saint-Herblain | France, Saint-Herblain, 1 Place Océane | 2014-01-31 | -- | 2014 | 1 | |
| Obfelden | Obfelden | Switzerland | 2002-04-21 | -- | 2002 | 1 | |
| Oscarshall | Oscarshall | Norway, Oslo, Oscarshallveien | 2017-08-28 | 2017-11-28 | 2017 | 1 | |
| Odéon Théâtre de l'Europe | Odéon Théâtre de l'Europe | France, 75006 Paris, Place de l'Odéon | 2023-05-12 | 2023-06-09 | 2023 | 1 | |
| Odda ungdomsskole | Odda ungdomsskole | Norway, Odda, Eidesmoen | 2006-11-15 | -- | 2006 | 1 | |
| Orkdal Samfunnshus | Orkdal Samfunnshus | Norway, Fannrem | 1978-11-22 | -- | 1978 | 1 | |
| Overholser Theatre | Overholser Theatre | United States of America, Ardmore | 1910-12-21 | 1910-12-21 | 1910 | 1 | |
| Obshtinski teatar Vazrazhdane | Obshtinski teatar Vazrazhdane | Bulgaria, Sofia, Sq. Petko Slaveykov 4 (пл. Петко Р. Славейков 4) | 1996-11-30 | -- | 1996 | 1 | |
| Oslo Rådhus | Oslo Rådhus | Norway, Oslo, Rådhusplassen 1 | 2009-03-28 | -- | 2009 | 1 | |
| Otto-Klenert-Schule | Otto-Klenert-Schule | Germany, Bad Friedrichshall, Rathausplatz 7 | 2006-02-18 | -- | 2006 | 1 | |
| Oscar Theatre | Oscar Theatre | Ireland, Dublin | 1980-04-07 | 1980-04-19 | 1980 | 1 | |
| Oulu | Oulu | Finland, Oulu | -- | -- | | | |
| Ogra | Ogra | Romania, Ogra | -- | -- | | | |
| Ornans | Ornans | France, Ornans | -- | -- | | | |
| Odder | Odder | Denmark, Odder | -- | -- | | | |
| Ostróg | Ostróg | Poland, Ostróg | -- | -- | | | |
| Opera House | Opera House | United States of America, Wyoming, Wyoming | -- | -- | | | |
| Ohgawara | Ohgawara | Japan, Ohgawara | -- | -- | | | |
| Oituz | Oituz | Romania, Oituz | -- | -- | | | |
| Ornö | Ornö | Sweden, Ornö | -- | -- | | | |
| Opole | Opole | Poland, Opole | -- | -- | | | |
| Osimo | Osimo | Italy | -- | -- | | | |
| Oppdal | Oppdal | Norway, Oppdal | -- | -- | | | |
| Obârşia | Obârşia | Romania, Obârşia | -- | -- | | | |
| Opera House | Opera House | United States of America, Telluride | -- | -- | | | |
| Olivenza | Olivenza | Spain, Olivenza | -- | -- | | | |
| Oravice | Oravice | Slovak Republic, Oravice | -- | -- | | | |
| Ocna Sibiului | Ocna Sibiului | Romania, Ocna Sibiului | -- | -- | | | |
| Oranienburg | Oranienburg | Germany, Oranienburg | -- | -- | | | |
| Oddfellows' Hall | Oddfellows' Hall | Australia, Wagga Wagga, Fitzmaurice Street | -- | -- | | | |
| Odessa | Одеса (Odessa) | Ukraine, Odessa | -- | -- | | | |
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