| Southborough to Smolyan | 1,330.54 mi (2,141.30 km) |
| Southborough to Sofia | 1,227.96 mi (1,976.21 km) |
| Southborough to Sopot | 1,288.35 mi (2,073.40 km) |
| Southborough to Sozopol | 1,420.51 mi (2,286.10 km) |
| Southborough to Sredets | 1,402.20 mi (2,256.62 km) |
| Southborough to Stamboliyski | 1,300.57 mi (2,093.07 km) |
| Southborough to Stara Zagora | 1,334.32 mi (2,147.38 km) |
| Southborough to Svilengrad | 1,384.28 mi (2,227.78 km) |
| Southborough to Svishtov | 1,275.75 mi (2,053.12 km) |
| Southborough to Targovishte | 1,341.43 mi (2,158.82 km) |
| Southborough to Teteven | 1,257.70 mi (2,024.07 km) |
| Southborough to Troyan | 1,277.65 mi (2,056.18 km) |
| Southborough to Tryavna | 1,310.84 mi (2,109.59 km) |
| Southborough to Tutrakan | 1,313.34 mi (2,113.62 km) |
| Southborough to Varna | 1,398.98 mi (2,251.45 km) |
