| Hardenberg to Oerlinghausen | 96.08 mi (154.63 km) |
| Hardenberg to Oestrich-Winkel | 187.14 mi (301.17 km) |
| Hardenberg to Offenburg | 289.11 mi (465.28 km) |
| Hardenberg to Oftersheim | 236.83 mi (381.14 km) |
| Hardenberg to Ohrdruf | 213.26 mi (343.21 km) |
| Hardenberg to Ohringen | 264.35 mi (425.43 km) |
| Hardenberg to Olbernhau | 316.48 mi (509.33 km) |
| Hardenberg to Olching | 365.76 mi (588.63 km) |
| Hardenberg to Oldenburg | 77.66 mi (124.97 km) |
| Hardenberg to Oldenburg in Holstein | 212.51 mi (342.01 km) |
| Hardenberg to Olfen | 67.12 mi (108.03 km) |
| Hardenberg to Olpe | 119.04 mi (191.58 km) |
| Hardenberg to Olsberg | 115.68 mi (186.17 km) |
| Hardenberg to Oranienburg | 277.64 mi (446.82 km) |
| Hardenberg to Ortenberg | 185.33 mi (298.26 km) |
