For 2 days (weekend) in St. Petersburg it is quite possible to have time to see the main sights of the city. First of all, this is the city center: Nevsky Prospekt, the monument to Catherine II in Catherine Square (local call it Katkin Garden), the Kazan Cathedral, the Bank Bridge over the Griboedov Canal, which guard the griffins. From there you can go to St. Isaac's Cathedral and climb onto its colonnade, then through the Alexander Garden go to the Senate Square to the Bronze Horseman

Either past the Cathedral of the Savior on Spilled Blood and the Engineering (Mikhailovsky) Castle in the direction of the Mikhailovsky Garden, and from there straight to the Summer Garden and further along Dvortsovaya Embankment to Dvortsovaya Square

In good weather you can ride along the canals and rivers of St. Petersburg, visit the Peter and Paul Fortress. It's time for dedicated museum days to be devoted to museums - one Hermitage will take a full day.

If you were in St. Petersburg from mid-May to early October, when fountains are working, on the second day, go to Peterhof. The fountains of Petrodvorets are something amazing. The excursion takes a day, at will you can visit some palaces and pavilions of this museum-reserve