| Donegal to Smolyan | 1,738.98 mi (2,798.62 km) |
| Donegal to Sofia | 1,635.22 mi (2,631.63 km) |
| Donegal to Sopot | 1,691.91 mi (2,722.87 km) |
| Donegal to Sozopol | 1,816.66 mi (2,923.64 km) |
| Donegal to Sredets | 1,800.18 mi (2,897.11 km) |
| Donegal to Stamboliyski | 1,707.13 mi (2,747.37 km) |
| Donegal to Stara Zagora | 1,736.38 mi (2,794.44 km) |
| Donegal to Svilengrad | 1,787.94 mi (2,877.42 km) |
| Donegal to Svishtov | 1,672.34 mi (2,691.37 km) |
| Donegal to Targovishte | 1,736.36 mi (2,794.40 km) |
| Donegal to Teteven | 1,661.31 mi (2,673.63 km) |
| Donegal to Troyan | 1,680.14 mi (2,703.93 km) |
| Donegal to Tryavna | 1,711.14 mi (2,753.81 km) |
| Donegal to Tutrakan | 1,703.27 mi (2,741.14 km) |
| Donegal to Varna | 1,789.97 mi (2,880.68 km) |
