| OAE |
1 |
| Oana Teodora Moldovan |
1 |
| obelisk |
3 |
| obol |
5 |
| Obrochishte |
1 |
| obsidian |
5 |
| obsidian blade |
1 |
| Obzor |
1 |
| OCBC (Office central de lutte contre le trafic de biens culturels) |
1 |
| oceanarium |
1 |
| ochre |
1 |
| Odeon |
15 |
| Odeon Plovdiv |
14 |
| Odessa |
1 |
| Odessos |
43 |
| Odessos Archaeological Preserve |
3 |
| Odessus |
30 |
| Odisseus |
1 |
| Odr |
1 |
| Odrin |
4 |
| Odrin Iconography School |
1 |
| Odrysae |
5 |
| Odrysian Kingdom |
57 |
| Odrysians |
48 |
| Odryssian Kingdom |
11 |
| Odryssians |
2 |
| Odysseus |
1 |
| Odyssey |
2 |
| Oedipus |
3 |
| oenochoe |
3 |
| Ofer Bar-Yosef |
1 |
| Ognen Nos (Fiery Cape) |
1 |
| Ognyan Tsenkov |
1 |
| Ognyanovo |
1 |
| Ogosta River |
1 |
| Ohio |
1 |
| Ohoden |
12 |
| Ohoden Neolithic Settlement |
1 |
| Ohrid |
4 |
| Ohrid Archbishopric |
1 |
| Ohrid Literary School |
10 |
| oil |
1 |
| oil painting |
1 |
| Okinawa |
1 |
| Okinawa Island |
1 |
| Okinawa Peace Memorial Museum |
1 |
| Olbia |
1 |
| Olbia Pontica |
1 |
| Old Bridge Svilengrad |
2 |
| Old Bulgarian |
18 |
| Old Bulgarian literature |
4 |
| Old Capitals Act |
1 |
| Old Capitals Association |
1 |
| Old Europe |
11 |
| Old Great Bulgaria |
13 |
| Old Metropolitan's Office in Veliko Tarnovo |
1 |
| Old Mill Balchik |
2 |
| Old Nessebar Museum |
3 |
| Old Sozopol Archaeological and Architectural Preserve |
2 |
| Old St. Peter's Basilica in Rome |
6 |
| Old Stone Age |
4 |
| Old Town |
2 |
| Old Town Dobrich |
1 |
| Old Town Nessebar |
3 |
| Old Town Plovdiv |
9 |
| Old Town Sozopol |
9 |
| Old Town Veliko Tarnovo |
2 |
| Old World |
1 |
| Oleg Alexandrov |
2 |
| oligarch |
3 |
| oligarchy |
3 |
| Oligocene |
1 |
| olive oil |
4 |
| Oliver Lodge |
1 |
| Olivier Picard |
1 |
| Oltenia |
2 |
| Oltenita |
1 |
| Olya Milanova |
5 |
| Omar Saidou Tall |
1 |
| omega |
1 |
| Onogur |
4 |
| Onsekiz Mart University |
1 |
| Opan Municipality |
1 |
| open-air museum |
28 |
| open-type settlement |
1 |
| opening |
4 |
| Operation Barbarossa |
1 |
| Operation Downfall |
1 |
| Operation Iceberg |
1 |
| opium |
1 |
| Oplontis |
1 |
| opus mixtum |
1 |
| opus tesselllatum |
1 |
| Oracle of Delphi |
1 |
| Oranta |
6 |
| Order of the Knights Templars |
1 |
| orders in classical architecture |
2 |
| ore |
1 |
| Orehovo |
2 |
| Oreshaka |
1 |
