A particular attraction is the luxury carriage used by Bulgaria's former king, Boris III (1918-1943). "So elegant and modest," gushed Rada Gancheva, 58.
The comforting hoots, whistles and puffs of steam trains have proved a big money spinner for Bulgarian State Railways (BDZ), earning it 250,000 euros ($280,000) last year.
"The Vitosha Express diesel train of (ex-communist dictator) Todor Zhivkov will soon be made available also," promised BDZ's chief executive Georgy Drumev.
However, this success belies the dire state of the railways in the European Union's poorest country.
According to a 2015 Boston Consulting Group study, Bulgarian trains have the worst quality and safety record among 25 European countries surveyed. The number of Bulgarians using trains halved between 2000 and 2015 and the volume of freight is a 10th of what it was in the 1980s, according to Georgy Minchev, of the freight transport association.
Creaking infrastructure and ageing locomotives and rolling stock mean that the average train speed is just 55 kilometres (35 miles) per hour. The 440-kilometre trip from Sofia to Varna on the Black Sea takes eight hours - and that's on the so-called "express train". "We started with a 40-minute delay and it grew to four hours by the time we arrived in Varna, making it a 12-hour journey," said one recent traveller, Maria Damyanova, 48.
Horror stories abound on the internet about people's experiences, particularly in winter when the simplest journey can turn into a nightmare.
"Iron nerves and plenty of food are needed if you want to take the train in Bulgaria," reads a typical social media entry by one disgruntled passenger, Margarit Blagoev, 35.