Route number is 21. Remember it—the number stays the same everywhere: on the stop display, in apps, on the vehicle itself. Look for 21 specifically. If you're not sure you found the right stop, just ask someone nearby: 'Does bus 21 stop here?'

This route serves the Sofia (Bulgaria) region. In larger metro areas, routes can pass through several districts or towns. To know for sure if it works for you, pull up the route map and check the key stops and direction.

Operator is Столичен автотранспорт. This is the official company responsible for the route. If you run into problems (rude driver, breakdown, dirty vehicle, delays)—contact them. It helps to note the time, direction, and route number—makes your complaint more specific and gets handled faster. Contact info is usually on the company website or in transit apps.

This route is part of the 'Градски транспорт София' transit system. Within one network, payment and transfer rules are often consistent. Terms can differ though, so check current fares and payment methods in up-to-date sources before your trip.