Sofia's public transport is getting better and new trams, trolley buses and buses are already running on some of the routes. It is fairly reliable except in the harshest winters and the lack of A/C or even any form of ventilation on some of the older trams and buses can be highly unpleasant in the summer months. Trams, trolley buses and buses cover the whole of the city, including the outskirts and are relatively inexpensive way to move around. Modern apps make it easier to navigate your way.
Sofia has two underground lines which intersect in the city centre at the Serdika stop. One line runs from the East (Sofia Airport or Business Park Sofia) to the West (Lyulin), via the city centre while the other, shorter, line runs from South to North (Nadezhda). 2020 will see the addition of part of the third line out to to Ovcha Kupel district from Patriarch Eftimii Blvd in the centre and eventually on to the Vasil Levski District. The underground is clean and efficient, though it does get crowded at peak times. Tickets cost 1.60 leva for a single journey and can be bought from the ticket machines at the entrance to the stations. An electronic card with 10 journeys priced at 12 leva (and rechargeable) is a better deal if you are a group (you just pass the card between you) or are spending more time in the city.
Bus, trolley bus and tram tickets can be bought for 1.60 lev from the machine just behind the driver's cabin. The ticket is only valid for the journey on that particular tram/bus. Daily, weekly and monthly travel cards can be bought from kiosks as can packs of 10 tickets, which need to be punched in the machine inside. The fine for not having a ticket is currently 20 leva and is payable on the spot.