Are you planning a trip from Sofia to Varna or vice versa?
Your options are to travel with your own car (if you have one), a shared ride (might not be the safest), a bus (that feels like an infinity), or by train.
Contrary to popular belief amongst most Bulgarians, a train ride might be the most enjoyable, relaxing and least stressful.
Here is the time to make a disclaimer. I would recommend the train ride only if you chose the “fast” overnight train in a sleeping compartment. Otherwise, some if these rides take a bit too much time to enjoy being confined to a seat.
The sleeping wagons are probably the newest in the Bulgarian railway and very nicely maintained. It is the closest you could get to a Western European experience in a Bulgarian train.
In the current situation with COVID-19, having the compartment only for myself was quite comforting and allowed me to fully relax and sleep like a baby through the whole ride from Sofia to Varna.
There are a few options to chose from. You could either share the compartment with one or two people, or pay the extra few leva (BGN) for the so-called business class which in essence is the same compartment only at your disposal.
There is a sink and a luggage hanger in each comparment. But beware there is no storage available for big pieces of luggage.
Bathrooms are shared, but quite neat and frequently cleaned.
A nice surprise was this initiative to promote reading(unfortunately only publications in Bulgarian available at the time).

Note: If you are traveling during the touristic season on the Bulgarian Blacksea coast, make sure to book in advance through the website of the Bulgarian railway.