... I made it to Belgrade!
I thought the journey would take 8.5 hours, but with the time difference between Bulgaria and Serbia it's actually 9.5 hours - and thanks to train delays it took me almost 12 hours!
I'm not quite sure what caused the delays, 2 x border control seemed to go pretty smoothly. However we stopped more times than the met line does - there were no announcements, not that I would have understood them even if there were.
What do you need to know if you're making the same journey?
Departure time: daily at 11.30am, or 6pm for the overnight train
Price: 50 lev (approx. £20) or around 70 lev for the overnight train
Journey time: 9.5 hours (if no delays)
Sofia station facilities: Not too bad, you can pick up snacks and sandwiches before departure
On-board comfort: considering the carriages are pretty old, the seats are fairly comfortable. I was lucky enough to have a cabin to myself for the entire journey so I could strech out and wonder about a bit. Apparently off-Season it's pretty usual for the trains to be as quiet as this
On-board catering: None
On-board toilet facilities: Very basic, no loo roll
To note: if you're travelling with a suitcase you'll attract the attention of the station helpers so make sure you have some small notes to hand to tip them. These guys are sort of in a uniform... pretty casual clothes, but all of there jackets have orange shoulders. I tipped 7 lev as that's what I had left in small notes. I was asked for a larger tip in Euros - I simply said no. 7 lev is enough to buy a good lunch in Hungary, so that was a generous tip as it was.