| Castricum to Olympia Heights (Florida) | 4,622.64 mi (7,439.43 km) |
| Castricum to Omaha (Nebraska) | 4,421.15 mi (7,115.15 km) |
| Castricum to On Top of the World Designated Place (Florida) | 4,526.88 mi (7,285.31 km) |
| Castricum to Onalaska (Wisconsin) | 4,120.35 mi (6,631.06 km) |
| Castricum to Oneida (New York) | 3,587.02 mi (5,772.75 km) |
| Castricum to Oneonta (New York) | 3,591.94 mi (5,780.67 km) |
| Castricum to Ontario (California) | 5,520.67 mi (8,884.67 km) |
| Castricum to Ontario (Oregon) | 4,919.03 mi (7,916.42 km) |
| Castricum to Opa-locka (Florida) | 4,610.08 mi (7,419.21 km) |
| Castricum to Opelika (Alabama) | 4,467.32 mi (7,189.46 km) |
| Castricum to Opelousas (Louisiana) | 4,837.97 mi (7,785.97 km) |
| Castricum to Orange (California) | 5,541.00 mi (8,917.37 km) |
| Castricum to Orange (Texas) | 4,923.35 mi (7,923.37 km) |
| Castricum to Orange City (Florida) | 4,495.37 mi (7,234.59 km) |
| Castricum to Orangeburg (South Carolina) | 4,247.34 mi (6,835.44 km) |
