Which route? Does it still exist?

6 hours is too short for any special trains (i.e. #001/2 is Moscow - St.Petersburg 8 hour night train) so you can expect that at any route, also attendants have to wake up passengers by a rule.

Added: GP is probably talking about a train that didn't cross a border.

I believe it was Krasnodar to Sochi, along the sea, so you'd wake up and look out and see nothing but ocean on one side.

This was like two years ago or so, so still exists probably