I remember travelling to Vilnius in the USSR by train from Poland in 1989. It was just as serious a border crossing with armed guards and high security as travelling by train across the Iron Curtain from West to East.
I flew to Warsaw, thinking I would be able to buy a ticket for the train onwards. I already had my USSR visa and Intourist hotel booking valid by the border crossing at Grodno as used by the daily train to Leningrad. I hadn't realised that tickets for the train were sold out well in advance and began panicking about how I could make the journey. One of the very few times I ever experienced a Polish person volunteer information without being asked was when the doorkeeper to the international ticket counter said 'but there is another train', after my fruitless attempts to buy a ticket at the counter in both English and German. Armed with this information, I was able to discover a handwritten slip of paper at the foot of only one of the information boards confirming the existence of a local train from Warsaw to Grodno, across the border in the USSR on dual gauge track. I purchased a cheap through ticket from Warsaw to Vilnius using Polish currency with no difficulty. The train left Warsaw about one hour after the through international train.
I joined the local train which emptied out as it moved Eastwards, until by the time we reached Bialystock there was almost nobody on board. The train headed off towards the Polish/USSR border and Polish border guards came through the train to check my papers. They took my double transit visa papers which was a bit concerning as to how I would be able to return home but offered no explanation as they spoke only Polish. The USSR border guards followed them through the moving train and processed my papers whilst the train was underway. I was one of very few passengers on board, besides being the only non-local passenger. Customs and visa checks were polite but very thorough. Panels were removed in the coaches to check for smuggled items. Armed guards were riding outside the carriages on the steps of the train wearing goggles to protect their eyes as we moved along at speed with watch towers along the border fence. The train pulled into Grodno station and I was one of the few passengers to get off. No sign of a train to Vilnius but the International train which had left Warsaw an hour or so before us was due to leave an hour or so later as it had been stopped at the border changing bogies. I had no idea if I would be able to catch it, or have to find a local service which may, or may not, operate on the line.
I was able to freely walk around Grodno with no idea what the city had to offer, and no roubles in my pocket, making sure only that I was back at the station in good time for the onward train which had left Warsaw before me but was now running on broad gauge rails.
When I arrived at the station, there was the train - all 18 coaches of it. My next problem was where I should sit, added to the worry as to whether my cheap handwritten ticket was even valid on the international train which could not accommodate me in Warsaw.
I decided to get into the last coach of the train as close to departure time as possible thinking the worst that could happen was that they would make me leave the train at the first stop, which was Vilnius, just where I wanted to be.
The female coach attendant came through the train checking tickets and checked mine without comment, moving on through the open coach. She seemed to get into a heated discussion with another passenger further along the coach and then broke off the check to return to me. She demanded my ticket again and took it away, much to my concern. The ensuing conversation further along the train then seemed to be along the lines of reprimanding the passenger who had been the centre of the discussion and showing him my ticket with a conversation which seemed to be along the lines of 'this is the ticket which you should have'. She returned to me with my ticket, smiles and grateful thanks. I had no idea what was going on and had originally expected it would have been me who had the ticket problems!
I was met in Vilnius station by my Lithuanian friends who took me to my hotel to check in and they carried out the formalities of hotel registration for me as I speak neither Russian nor Lithuanian. There seemed to be some concern over the transaction and I enquired what was the problem. I was told that the hotel had been told that I was not coming because I was not on the train when it crossed the border. I had done everything by the book and there were no problems, but big brother truly was watching very closely.