| Castro Valley to Smolyan | 6,571.17 mi (10,575.28 km) |
| Castro Valley to Sofia | 6,470.91 mi (10,413.93 km) |
| Castro Valley to Sopot | 6,505.91 mi (10,470.26 km) |
| Castro Valley to Sozopol | 6,583.23 mi (10,594.68 km) |
| Castro Valley to Sredets | 6,577.16 mi (10,584.92 km) |
| Castro Valley to Stamboliyski | 6,533.23 mi (10,514.22 km) |
| Castro Valley to Stara Zagora | 6,539.10 mi (10,523.66 km) |
| Castro Valley to Svilengrad | 6,592.74 mi (10,610.00 km) |
| Castro Valley to Svishtov | 6,458.65 mi (10,394.20 km) |
| Castro Valley to Targovishte | 6,507.63 mi (10,473.01 km) |
| Castro Valley to Teteven | 6,478.63 mi (10,426.35 km) |
| Castro Valley to Troyan | 6,490.66 mi (10,445.71 km) |
| Castro Valley to Tryavna | 6,508.74 mi (10,474.80 km) |
| Castro Valley to Tutrakan | 6,457.96 mi (10,393.08 km) |
| Castro Valley to Varna | 6,536.91 mi (10,520.14 km) |
