Metro!

The Metro in both St. Petersburg and Moscow is really something to write home about - as positively as possible. Especially in comparison with London's Tube. It's highly efficient for starters: even in a busy city like Moscow with its extensive Metro network I don't think I've ever waited for longer than two (2) minutes and something for a train. I know because there's a clock that resets every time a train comes. Three minutes is minimum wait in London, I think. I haven't seen any signals fail. Trains haven't been standing on the tracks for no apparent reason. All trains are old but, hell, they work well.
On top of all that, there are the stations themselves. Meny are monumental - literally - with mosaics or iron sculptures or reliefs and domed ceilings. They are sights in themselves, actually. It makes using the metro a real experience.
Finally, it's even quite cheap. 17 rubles even in Moscow with a discount for carnet tickets.
Sorry, but eat your heart out TfL.