The nearest to the Ioffe Institute hotels are
These hotels are located within walking distance (1 km) to the Ioffe institute. Hotel "Orbita" is located right next to the Metro station "Ploschad' Muzhestva" and hotel "Sputnik" in two bus stops from the Metro station "Ploschad' Muzhestva" (see map).
You can book a hotel not only on the booking.com but also on the hotel website. Information on the room availability at the hotel's site may not match the information on the booking.com. Despite the fact that the hotels are booked by the participants themselves, organizing committee will be glad to help foreign participants in case of doubt about the vacant rooms in these hotels.
It won't take more than half an hour to get to the conference venue near Politekhnicheskaya subway station (the red line "M1") from the central subway stations such as Chernyshevskaya, Ploshad Vosstania, Vladimirskaya or Nevsky Prospekt. Mind the time needed to get from your hotel to the nearest subway station. It's not always necessary to use public transportation to get to the subway station in the downtown, it's faster to walk there.
See St.Petersburg metro map for additional information.