Engineers and railway enthusiasts may find this moderately interesting...
After crossing the border into China and surrendering our passports to the authorities, the train rolls into huge shed for a couple of hours.
The bogeys need changing. Huh? Railway gauges are not standard. The European, Indian and Chinese are common, but the Russian rails are 5" further apart. So, in order to facilitate an international service between Mongolia and China, the carriages are separated and jacked up in sync, while the old wide bogeys are rolled out, and the new narrower ones are rolled.
Once fixed, and with much juddering and jolting, creaking and crashing as the carriages are reattached, we roll back to the border station, and three hours later, with paperwork complete, our passports are returned and we're now in China...Time for bed.
It used to be strictly forbidden to take photos here, but I think the secret's out.