| Harpenden to Olivares | 1,034.22 mi (1,664.41 km) |
| Harpenden to Olivenza | 963.84 mi (1,551.15 km) |
| Harpenden to Olot | 678.93 mi (1,092.62 km) |
| Harpenden to Onate | 614.48 mi (988.92 km) |
| Harpenden to Onda | 819.11 mi (1,318.23 km) |
| Harpenden to Onteniente | 897.97 mi (1,445.15 km) |
| Harpenden to Orihuela | 949.22 mi (1,527.62 km) |
| Harpenden to Osuna | 1,033.89 mi (1,663.88 km) |
| Harpenden to Ourense | 743.41 mi (1,196.41 km) |
| Harpenden to Oviedo | 637.50 mi (1,025.96 km) |
| Harpenden to Paiporta | 856.05 mi (1,377.68 km) |
| Harpenden to Pajara | 1,769.99 mi (2,848.53 km) |
| Harpenden to Palafolls | 716.23 mi (1,152.66 km) |
| Harpenden to Palafrugell | 703.68 mi (1,132.47 km) |
| Harpenden to Palamos | 708.14 mi (1,139.64 km) |
