| Irthlingborough to Smolyan | 1,394.66 mi (2,244.49 km) |
| Irthlingborough to Sofia | 1,291.29 mi (2,078.14 km) |
| Irthlingborough to Sopot | 1,349.63 mi (2,172.02 km) |
| Irthlingborough to Sozopol | 1,478.07 mi (2,378.73 km) |
| Irthlingborough to Sredets | 1,460.65 mi (2,350.69 km) |
| Irthlingborough to Stamboliyski | 1,363.56 mi (2,194.44 km) |
| Irthlingborough to Stara Zagora | 1,394.83 mi (2,244.76 km) |
| Irthlingborough to Svilengrad | 1,445.71 mi (2,326.64 km) |
| Irthlingborough to Svishtov | 1,333.34 mi (2,145.81 km) |
| Irthlingborough to Targovishte | 1,398.29 mi (2,250.33 km) |
| Irthlingborough to Teteven | 1,318.98 mi (2,122.69 km) |
| Irthlingborough to Troyan | 1,338.33 mi (2,153.84 km) |
| Irthlingborough to Tryavna | 1,370.39 mi (2,205.42 km) |
| Irthlingborough to Tutrakan | 1,367.76 mi (2,201.19 km) |
| Irthlingborough to Varna | 1,454.03 mi (2,340.03 km) |
