| Boulder to Smolyan | 5,984.58 mi (9,631.26 km) |
| Boulder to Sofia | 5,880.82 mi (9,464.27 km) |
| Boulder to Sopot | 5,926.48 mi (9,537.75 km) |
| Boulder to Sozopol | 6,026.00 mi (9,697.90 km) |
| Boulder to Sredets | 6,015.43 mi (9,680.89 km) |
| Boulder to Stamboliyski | 5,948.82 mi (9,573.70 km) |
| Boulder to Stara Zagora | 5,965.40 mi (9,600.38 km) |
| Boulder to Svilengrad | 6,019.28 mi (9,687.10 km) |
| Boulder to Svishtov | 5,890.07 mi (9,479.16 km) |
| Boulder to Targovishte | 5,946.50 mi (9,569.96 km) |
| Boulder to Teteven | 5,897.14 mi (9,490.53 km) |
| Boulder to Troyan | 5,912.45 mi (9,515.18 km) |
| Boulder to Tryavna | 5,936.58 mi (9,554.00 km) |
| Boulder to Tutrakan | 5,902.11 mi (9,498.53 km) |
| Boulder to Varna | 5,986.37 mi (9,634.13 km) |
