Yes, Baltics was also my first impression. Maybe also Poland, but no further.
The big church well visible in some panoramic pictures is a lot like Niguliste in Tallinn, but it is not it. I will try to google for cathedrals in Baltics later, as there is not many possibilities for such a big church in those small countries.
I also tried to find signs and texts in the pictures that could help with locationing, but could not find anything. Soviets were masters in hiding nationalities.
I also took some blowups of cameras in the pictures:
http://www.ussrphoto.com/UserContent2/742019_000000720001190401.jpgZarya? 85mm tele?
http://www.ussrphoto.com/UserContent2/742019_000000790007190401b.jpgZenit E? Jupi-135mm?
http://www.ussrphoto.com/UserContent2/742019_000000790013190401b.jpgFolding camera? No idea what, maybe Iskra, never had one?
http://www.ussrphoto.com/UserContent2/742019_000000820016190401b.jpgFED or Zorki retractable lens?
Personally I found two very interesting pictures.
One has most likely a Vjatka-3 Elektron which is Vespa-copy and made 1973-1979.
The other is the Moskvitch pedal car, also popular in Finland.
And the Horizont pictures with balloons are most likely taken 1st of May.
Best regards,
Juhani