The Trans-Mongolian Railway connects Russia with China via Mongolia. The railway operates clean and comfortable Chinese trains,with a range of accommodation options.
There is a buffet car onboard, and each train has its own security patrol to make sure everyone is safe and secure. The trains are generally kept pretty warm, so you will need to bring clothing suitable for the cold outdoors, as well as the toasty interior. Plug sockets (220V - European-style) are sometimes available in the corridors, but you will have to compete with other passengers to use them. Sometimes the power doesn't work. Occasionally, conductors will offer to charge your devices for you in their own compartments (for a price!).