From Helsinki it is only a 5 hour train ride to St. Petersburg, so I took the opportunity to stay a week-end here while being at some meeting in Finland. Being on your own is a little bit tricky with no knowledge about the Russian language - but as experienced traveler I got around ;-) My insider tip is the Antique Hotel Rachmaninov, next to the Kazan cathedral - small but very nice rooms and located only footsteps away from the Nevsky prospect.
This is the main square of St. Petersburg where some important events in Russian history took place. The Eremitage is the largest art museum in the world. Bring a lot of time...
Located between the Neva and the Nevsky Prospect this church was erected at the site where Alexander II was assassinated. You can find lots of paintings and mosaics inside.
The third largest cupola in the world - walk up to the rotunda to enjoy fantastic views of St. Petersburg.
On the other side of the Neva, visit the Peter and Paul Fortress. The ramparts walk offers nice views of the riverside.