Note
4.86 miles - walking from the hotel to the Neviskiy Prospect metro station & then from the Chkalovskaya metro station via a number of Style Moderne buildings (on Bolshaya Zelenina Ultisa and Kamennoostrovsky Prospect), then back over Troitskiy Most to the gates of the Summer Garden & then back through the Field of Mars and via the Church on Spilled Blood to the hotel. I would have gone for a bit longer walk, but I needed to get back to the hotel to find out whether they'd recovered my passport (having given it to a stranger) and put pressure on them if they hadn't; luckily they had.
Then more walking in St. Petersburg & Heathrow (T5) airports.