The Moscow subway system is really interesting. These photos don't do it justice. I'm sure there is a ton of info online in regards to the history of the system. Built by the Soviets the subway system is a working monument for the common people.

Most stations are super clean, spotless, I couldn't believe how clean they are. NYC stations are filthy and dusty. Moscow's stations don't have the dusty grime that is ubiquitous in NYC stations. Trains came quickly and efficiently, never a problem. The trains themselves were really old and seemed to work just fine.
The stations pictured below are regular stations packed with people and heavily used everyday, not just for tourists like San francisco cable cars, really impressive.

Almost all the platforms were about double to triple the width of a station here in NYC and the ceilings were much higher.

Above is a relatively simple station, and even here the materials are impressive. Materials at almost every station I visited were top notch, marble, granite, and other types of stone expertly laid out and very well maintained.

Impressive metal work.

Details were amazing. Notice no grime and dust.

Station dedicated to Dmitry Mendeleyev inventor of The Periodic Table of Elements. I didn't get a photo, but another version of these "molecule" inspired lamps were also on the platform where the trains stopped, very nicely done.